A Complete Breakdown of Custom System Development Costs: What Separates NT$500K from NT$5M

What Is Custom System Development

Custom system development means building a dedicated software system from scratch around your company's own business processes, rather than adopting an off-the-shelf SaaS product or ERP module from the market.

Its core value comes down to a single sentence: existing tools can't precisely support your business logic, so you need a system designed solely for you.

This is not about being "more advanced than SaaS," nor is it "only for large enterprises." A 50-person manufacturing plant, an 80-person logistics provider, a 120-person chain service business—any of them can reach the tipping point where customization becomes necessary. The criteria are simple:

• Does your team do a lot of manual integration in Excel every day, work that off-the-shelf systems simply can't handle?
• Does your business process have unique rules that force a market SaaS to require extensive custom configuration just to barely work?
• Are you maintaining two or more manual processes because your systems can't connect to each other?

If two of these three questions are a yes, you've probably reached the point where you should seriously evaluate custom development.

How Costs Are Calculated: The Four Core Variables Behind a Quote

When many companies inquire about custom development for the first time, they ask directly, "I want to build a system—roughly how much will it cost?" Then they receive four wildly different quotes from four vendors, ranging anywhere from NT$300K to NT$3M, with no way to compare them.

The reason is this: the cost of a custom system has never been determined by a "feature list." It is determined jointly by the following four variables.

Variable One: The Complexity of Business Logic

Business logic refers to the degree to which your system needs to understand and execute your company's internal rules.

For example, "recording an order" is a feature. But "automatically calculating discounts and triggering different approval workflows based on customer tier, order quantity, that week's promotions, and the salesperson's assigned territory" is a piece of complex business logic.

The latter may require three to five times the development time of the former—yet on a requirements list, both are written down as nothing more than "order management."

This is where the cost of custom development is most often underestimated. Based on development experience across more than five hundred projects, TWJOIN has observed that 65% of custom system projects that overrun their budget trace the root cause back to the requirements-definition stage: the company only discovers after development begins that the actual business logic is more than three times as complex as originally described.

Variable Two: The Number and Depth of Integrations

Which existing tools does your new system need to connect with? ERP, CRM, financial systems, e-commerce platforms, logistics APIs, government filing systems?

Every integration point means studying the other party's API specifications, handling data format conversions, testing edge cases, and dealing with error responses. A single integration point typically adds somewhere between NT$50K and NT$200K, depending on how open the other system is and how complete its documentation is.

If you need to integrate three or more external systems, the integration cost often exceeds the core features themselves.

Variable Three: The Layers of Roles and Permissions

How many user roles must the system support? What can each role see and do, and are there fine-grained differences between them?

A system used only by internal employees, all with identical permissions, has the simplest architecture. Once you add requirements like "manager approval," "customer self-service portal," "supplier credential uploads," or "cross-company multi-tenancy," the complexity of the system architecture grows exponentially, and development time can increase by 40%–80%.

Variable Four: The Expected Frequency of Future Changes

If your business rules are very stable, the work can be completed quickly with a lighter architecture. If you anticipate major shifts in your business model over the next two years, you'll need more flexibility designed in at the architectural level—higher upfront cost, but dramatically lower cost of changes later.

Ignoring this variable is one of the main reasons many companies find that "the system needs a major overhaul just two years after it's finished."

What Separates an NT$500K, NT$1.5M, and NT$5M System

Below are three budget tiers TWJOIN has compiled from real cases, to help you build a basic mental framework for costs.

NT$500K – NT$1M: A Single-Function Internal Management Tool

Best for: lightweight systems that solve a single pain point—an internal leave-approval workflow, a simple order-tracking back office, a supplier data management system.

Typical specs:

• 1–2 core feature modules
• 2–3 user roles
• Little to no external system integration
• Relatively simple business logic with fixed rules

Note: A system within this budget has very tight feature focus. If your requirements list runs more than three A4 pages, this budget is most likely insufficient. Don't try to "cram lots of features" into this budget—the result is that every feature ends up half-baked.

NT$1M – NT$2.5M: A Mid-Sized Business System

Best for: systems that need complete back-office management and carry a certain degree of business-logic complexity—a membership points and tier management system, a multi-warehouse inventory system, a booking, scheduling, and resource management platform for the service industry.

Typical specs:

• 4–8 feature modules
• A complete back-office management interface
• 1–3 external system integrations (such as payments, logistics, ERP)
• Business logic of moderate complexity
• Basic data reporting included

Note: This budget tier is the main range for custom development among mid-sized Taiwanese enterprises. It has the most competing vendors and the widest variance in quotes, so a sharp eye in vendor selection matters especially here. A later section is dedicated to how to evaluate vendors.

NT$2.5M and Above: Complex Business Systems or Platforms

Best for: business platforms involving complex business logic, multi-organization structures, extensive system integration, or high-traffic handling—a multi-brand, multi-channel order management hub, a B2B procurement platform, a multi-tenant SaaS system prototype.

Typical specs:

• Cross-department or cross-organization business process integration
• Complex permission architecture (multiple roles, multi-level approvals)
• Four or more external system integrations
• Highly customized business logic
• System architecture design that accounts for performance and security

Note: For projects at this tier, the quality of requirements definition directly determines success or failure. We recommend an independent requirements-discovery consulting engagement before formally awarding the contract—typically NT$100K–NT$300K, the most cost-effective investment in the entire project.

When You Should Choose Custom, and When SaaS Is Enough

There's no absolute answer to this question, but there is a clear decision framework.

When to choose SaaS:

• Your business processes are close to industry standards and don't need many special rules
• Your team is small with limited IT capability and needs something ready out of the box
• You're still figuring out your business model; requirements aren't settled and shouldn't be locked into a custom system
• Your budget is under NT$500K and SaaS can cover all your core needs

When to choose custom:

• Your business processes have unique logic that SaaS can't accurately support, requiring extensive manual patching
• You have data sovereignty requirements and don't want core business data stored on a third-party cloud
• You need deep integration with existing systems that have no corresponding API
• Over the long run, SaaS licensing fees plus labor costs add up to a five-year total that already exceeds the cost of custom development

A useful rule of thumb for estimating: if your current SaaS solution's annual licensing fees plus the labor waste caused by an ill-fitting system together exceed NT$500K, then within three years you may have recouped the cost of a low-to-medium-complexity custom system.

Five Key Questions for Choosing a Vendor (Ask These First, Then Ask About Price)

When many companies evaluate vendors, their very first question is "what's your quote?" That order is wrong.

Before asking about price, ask these five questions. How a vendor answers will tell you a great deal about their capability and integrity.

Question One: Have you built systems for industries similar to ours? Can we talk to those users?

Why ask: industry experience determines how quickly a vendor understands your business logic. A vendor who has built five logistics systems can ask sharper questions during requirements interviews than one who has never touched logistics.

What to listen for: a good vendor proactively offers cases and may even help arrange user interviews. If they hesitate or only say "it's confidential, we can't share," press for the reason.

Question Two: What is your requirements-interview process? How much time will you spend on requirements definition?

Why ask: the quality of requirements definition is the single most important investment in the entire project. A rigorous vendor spends at least two to four weeks on requirements interviews, ultimately producing a requirements document (Spec) with clear functional specifications, and only begins development after you confirm it.

What to listen for: if a vendor says "we'll build first and adjust whatever you want to change afterward," that's a high-risk way of working that almost certainly overruns both budget and schedule.

Question Three: How are you planning the technical architecture for this project? If I want to add features in the future, what's the process?

Why ask: the technical architecture determines the system's maintainability. What you're building now isn't just a system—it's an asset that must keep evolving three to five years from now.

What to listen for: a good vendor can clearly explain the rationale behind their technology choices and the possible paths for future expansion. Be especially cautious of those who can't explain it clearly, or who say "you don't need to understand this."

Question Four: How will we confirm progress during development? How do you handle requirement changes?

Why ask: progress transparency and a change-management process are the key mechanisms that determine whether the project ultimately meets expectations.

What to listen for: a good vendor has clearly defined milestones, regular progress-review meetings, and a written change-management process (requirement changes mean re-estimating hours, executed only after both sides confirm). Without this mechanism, the later stages of a project easily devolve into "more and more requirements, higher and higher costs, and an endlessly postponed completion date."

Question Five: After the system goes live, what does the maintenance contract cover? Who owns our data and source code?

Why ask: many companies only discover after go-live that ownership of the source code is in dispute, or that maintenance costs are far higher than expected.

What to listen for: normally, the source code of a system that the client paid to develop should belong to the client. If a vendor says otherwise, this needs to be explicitly clarified in the contract. The contents of the maintenance contract (which services are included, how it's billed, response-time commitments) also need to be settled clearly before signing.

Three Common Failure Scenarios in Custom Development

In the course of helping mid-sized enterprises with system evaluations and taking over rescue cases, TWJOIN has observed the following three recurring failure patterns. Understanding these patterns offers more protective value than any vendor-evaluation technique.

Failure Scenario One: Starting Development Before Requirements Are Clearly Defined

The plot: the company is in a hurry for the system, the vendor says "build first, adjust later," and the requirements document is just a three-page slide deck. Halfway through development, the company discovers many details it never thought of and keeps requesting changes. In the end the system costs 40% more than planned, goes live three months late, and the features are still incomplete.

The root cause: time saved on requirements definition is spent at triple the cost on remediation during the development stage.

The safeguard: require the vendor to produce a complete requirements-specification document before signing (including a feature list, business-logic descriptions, user flow diagrams, and a first draft of the data structure), and only move into development quoting after it's confirmed. This document itself can also serve as a basis for comparing the capabilities of different vendors.

Failure Scenario Two: Choosing the Lowest Bidder

The plot: among three vendors, the lowest quote is 40% below the highest. The company picks the lowest bid, and the vendor keeps adding "this wasn't in the original requirements" throughout development. The final total exceeds the second-lowest quote, and the quality is worse.

The root cause: the lowest bidder usually offered an "attractive number" when requirements were unclear, then recovers margin through add-on requirements. Or their engineers lack seniority and underestimated the workload.

The safeguard: require every vendor to quote on the basis of the same requirements-specification document, so the quotes are comparable. When ruling out the lowest bid, it's not that "expensive equals good"—it's that you need to understand the reasons behind the cost differences.

Failure Scenario Three: The Vendor Disappears After the System Is Finished

The plot: after the system passes acceptance, the vendor downsizes or pivots, and the maintenance contact vanishes. When something goes wrong with the system, there's no one to fix it; when the business needs a new feature, no one can take it over. The company is trapped: "can't use the old vendor, and a new vendor can't take it on."

The root cause: when choosing the vendor, they didn't evaluate the vendor's operational stability, nor did they require delivery of the source code and complete technical documentation.

The safeguard: stipulate clearly in the contract the source-code delivery terms, the completeness requirements for technical documentation (including system architecture descriptions, database structure, deployment instructions), and the maintenance responsibility period after go-live. When evaluating a vendor, also ask how many years they've been established and how stable their core team is.

Frequently Asked Questions (FAQ)

Question One: How long does custom system development take to complete?

A: It varies by complexity. A lightweight system in the NT$500K–1M range typically takes 3–5 months from requirements definition to go-live; a mid-sized system in the NT$1M–2.5M range takes about 5–8 months; a complex system above NT$2.5M may have a full development cycle of 8–18 months. These estimates assume that requirements are clearly defined and that no major requirement changes occur along the way.

Question Two: After custom development is complete, how is the maintenance fee calculated?

A: Maintenance fees usually follow one of two models: a monthly subscription (a fixed monthly maintenance fee that includes a certain number of modification hours), or time-and-materials billing (you pay only when you have a need). A monthly subscription is usually around 10%–15% of the development cost per year—for example, a NT$1.5M system has an annual maintenance fee of roughly NT$150K–NT$220K. Which model you choose depends on how frequently you expect to modify the system after go-live.

Question Three: My company only has 30 people—do we need a custom system?

A: Company size isn't the criterion; business complexity is. A 30-person company, if its business processes are highly unique (such as special custom-pricing logic or complex scheduling mechanisms), may need a custom system more than a 200-person standardized manufacturing plant. The way to judge is: how much labor are you currently spending to manually "patch" the gaps in your system? If that labor cost exceeds NT$500K a year, it's worth seriously evaluating.

Question Four: What is the core difference between a custom system and buying an ERP or CRM?

A: ERP and CRM are products designed around general best practices, able to cover 70%–80% of standard business needs—but that 20%–30% of difference is often exactly where your core competitiveness lies. The advantage of a custom system is that it maps 100% to your business logic, but it requires a longer build time and a higher upfront investment. The two aren't mutually exclusive: for many companies the best answer is "ERP handles financial accounting, the custom system handles core business processes, and the two connect via API."

Question Five: How do I ensure a custom system development doesn't end up abandoned halfway?

A: The three most effective protective mechanisms: (1) complete requirements definition, documented in writing and confirmed by both parties before development begins; (2) a clear milestone-based payment mechanism set in the contract, rather than a lump sum or payment based purely on time; (3) contractual assurance of source-code ownership and the complete delivery of technical documentation. All three can be clearly agreed when negotiating the contract—and if a vendor objects, that's a signal worth thinking hard about.

Conclusion: Time Spent on Requirements Discovery Is the Most Cost-Effective Investment in the Entire Project

Custom system development is, in essence, an investment in enterprise infrastructure—not a one-time procurement.

TWJOIN's hands-on experience tells us this: before building custom, the money most worth spending is spent on requirements discovery, not on driving down the development quote. Spending three extra weeks and an extra NT$100K at the requirements-definition stage can often save three months of time and more than NT$500K in add-on costs during the development that follows.

If your company is evaluating whether it needs custom system development, or already has preliminary system requirements but isn't sure where to start, you're welcome to contact TWJOIN for an initial requirements consultation. We provide a structured requirements-discovery service to help you clearly define requirements and accurately estimate costs before formally commissioning development.