How to Calculate the Real Cost of a SaaS Integration Before You Build It

The quote you get for a SaaS integration is almost never the number you’ll pay. Not because agencies are dishonest – though some are – but because integrations have a structural cost problem that doesn’t show itself until you’re already three weeks in. The API docs looked clean. The endpoint did what you needed. And then you hit the rate limits, the undocumented auth edge cases, the webhook payloads that don’t match the schema, and the support queue that takes four days to respond. By that point, the budget is half-spent and you’re still not in production.

We’ve shipped enough integrations to know: the stated API complexity is rarely the actual complexity. What follows is how we actually cost these builds, and what you should be asking before you sign anything.

Why Standard Integration Quotes Fall Apart

Most fixed quotes for integrations are based on the happy path. Developer reads the docs, sees the endpoint, estimates hours, adds a buffer, sends you a number. The problem is the buffer almost never accounts for the right things.

What actually blows out integration budgets:

• Auth that behaves differently in production than in sandbox – OAuth flows that work in Postman and break in real environments, token refresh logic that isn’t documented, session timeouts that aren’t mentioned anywhere.
• Rate limiting that isn’t clearly published – You find out about the 100-requests-per-minute cap when your first real user hits it.
• Payload inconsistency – The webhook says it sends a customer_id. Sometimes it sends null. Now you need defensive handling you didn’t plan for.
• Versioning gaps – The docs you read were for v2. The endpoint the third party actually supports for your tier is v1.8. Different fields, different behaviour.
• Error handling they’ve offloaded to you – Some APIs return a 200 status with an error message in the body. You won’t catch that with standard error handling.
• Their infrastructure instability – One payments API we integrated with had a known latency issue on their end during peak hours. Our client’s users thought our product was broken.

None of this is exotic. These are the normal conditions of building against someone else’s system. And none of them are visible in a quote that’s based on reading documentation.

The Three-Layer Cost Model We Use

When we scope an integration for a client, we break cost into three layers that most quotes collapse into one.

Layer 1: The integration itself. This is the direct build – authentication, data mapping, request/response handling, error states, retry logic. For a well-documented, stable API (think Stripe, Xero, Twilio), this is roughly $3,000-$8,000 AUD depending on the number of endpoints and the complexity of data transformation. For a messier API – something industry-specific, less maintained, or with partial documentation – you’re looking at $8,000-$20,000 before you’ve touched anything else.

Layer 2: The resilience layer. This is what turns a working demo into a production system. Queuing, retry mechanisms, dead-letter handling, monitoring and alerting when the third-party goes down, graceful degradation so your app doesn’t break when theirs does. Founders consistently underinvest here. It adds anywhere from 40-80% on top of Layer 1 costs, and skipping it is exactly how you end up with a 2am incident three months after launch.

Layer 3: Ongoing maintenance. APIs change. The third party ships a breaking change, deprecates an endpoint, updates their auth flow. Someone needs to be watching for that, and someone needs to fix it quickly when it hits. We tell clients to budget $500-$2,000 AUD per month per active integration for maintenance, depending on how critical the dependency is and how frequently the provider ships changes.

Add those three layers up for anything non-trivial and you’re often looking at $15,000-$40,000 AUD all-in for a single integration over its first twelve months. That’s not a complaint – it’s the honest number. And it’s the number that lets you make a real decision about whether the integration is worth building at all.

How to Assess API Quality Before You Commit

You can learn a lot about a third-party API before your developer writes a single line of code. Here’s what we check in the first few hours of evaluation:

1. Changelog recency. When did they last update their docs? An API with a changelog that stopped two years ago is either perfectly stable or quietly abandoned. You need to know which.
2. Community forum signal. Search their developer forum or GitHub issues for the specific endpoints you need. If there are multiple threads about the same edge case, you’ve found your first scope risk.
3. Sandbox fidelity. Does their sandbox behave the same as production? Ask them directly. If the answer is “mostly”, that’s a red flag.
4. Rate limit documentation. If rate limits aren’t clearly documented, assume they’re restrictive and build a queuing layer anyway.
5. Error response schema. Request a few intentional failures in the sandbox. How consistent are the error responses? Do they follow a standard format or are they ad hoc?
6. SLA and status page. Does the provider have a public status page? What’s their uptime history? What’s their incident response time? This is your dependency risk in plain sight.

This evaluation shouldn’t take more than a day of a senior developer’s time. If it takes longer, that’s itself a signal about what you’re dealing with.

The Build vs. Buy Question You Should Ask Earlier

Sometimes the right answer to “how much will this integration cost?” is “don’t build it custom at all.” There’s an entire category of integration work that middleware platforms like Zapier, Make, or dedicated iPaaS tools handle adequately – and for non-critical, low-volume workflows, paying $100-$500 AUD per month for a no-code connector is a better decision than spending $25,000 building it bespoke.

The cases where custom integration is unambiguously worth it:

• The integration is in the critical path of your core product – it’s not a nice-to-have, it’s what the product does.
• Data volume or frequency exceeds what a middleware tool handles reliably.
• You need custom transformation logic that a visual tool can’t express cleanly.
• You’re handling sensitive data where you need to control exactly what’s stored and where.
• The third-party API isn’t supported by the major middleware platforms.

We’ve had clients come to us with a $30,000 integration request that we’ve redirected into a $200/month Make setup. We’ve also had clients using Zapier for workflows that had grown complex enough to be genuinely costing them in reliability and engineering time to patch. Knowing which situation you’re in requires an honest assessment of the workflow, not just a preference for custom code.

What a Proper Integration Scope Document Should Include

If you’re commissioning an integration build, the scope document you receive from an agency should give you enough detail to understand what you’re buying. If it doesn’t include these elements, push back:

• A named list of the specific API endpoints being integrated, not just “Xero integration”
• The data transformation logic – what’s coming in, what’s going out, what’s being mapped to what
• How errors will be handled, including specific failure scenarios
• Whether a queuing or retry layer is included or out of scope
• What monitoring and alerting is included post-launch
• What’s excluded – specifically what happens if the third-party API behaves differently than documented
• How scope changes will be priced if you hit an undocumented edge case

That last one matters more than founders expect. An integration scope written at the doc-reading stage will always encounter reality differently. The question isn’t whether scope will shift – it’s how the engagement handles it when it does.

When to Have This Conversation

The founders who end up with integration blowouts are almost always the ones who scoped the integration too late. It becomes line item three in a larger build, gets quoted in a rush, and nobody really digs into the third-party API until development is underway.

If a third-party integration is load-bearing for your product – meaning your product doesn’t work properly without it – it deserves its own discovery sprint before anything else is scoped. Not after the platform architecture is decided. Not alongside the front-end build. Before.

That’s not a way to slow things down. It’s actually how you move faster, because you find the hard problems while you still have room to make decisions about them.

If you’re looking at an integration that makes you nervous, or you’ve received a quote that feels like it’s missing something, talk to Amora about your build. We’ll tell you honestly what we’d cost it at and where the risks sit – before you’ve committed to anything.