What system integration really costs

Ask three vendors to connect your ERP to a new customer portal and the quotes can differ by a factor of ten. That usually isn’t because anyone is overcharging. “Integration” can mean anything from a file copied across once a night to a real-time exchange that has to be accurate and auditable, and the brief rarely says which one is needed.

Where the money actually goes

Making the connection is the cheap part. Most of the cost sits in five areas.

Understanding the source system

What an API returns isn’t always what the business means by it. Fields get reused, status codes collect history, and one flag can mean three different things depending on which department created the record. Time spent here is how you avoid an integration that passes testing and then fails in production.

Agreeing what counts as the same record

Two systems rarely agree on identity. Is a customer a person, an account or a billing relationship? What happens when the ERP has one record and the CRM has two? Someone has to decide, and it is a business decision that engineers can’t make on their own.

Handling failures

This is where quotes differ most. If the other system is down for four hours, do messages wait, retry, expire or alert someone? Can the same message arrive twice without charging a customer twice? Retries, duplicate protection and the ability to replay failed messages make up most of the work in a serious integration, and none of it shows up in a demo.

Tracing problems

When finance reports a missing transaction, how long does it take to find where it stopped? Without shared reference IDs and searchable logs, the answer is days, and every later incident costs the same again.

Keeping up with change

Both systems will change over time. Versioned interfaces, a clear compatibility policy and tests that run against both sides decide whether the next upgrade is routine or another project.

Why the cheapest quote is cheap

Usually because it only covers the case where everything works. That can be a reasonable choice for low-value data that is easy to correct; syncing a marketing list doesn’t need the same guarantees as a payment. It isn’t reasonable for anything involving money, stock, access rights or regulated records.

So before comparing prices, compare what each quote includes in the five areas above.

Questions that make quotes comparable

• What happens if the other system is unavailable for an hour? For a day?
• Can the same event be delivered twice, and what stops it having an effect twice?
• Where do failed messages go, and who is alerted?
• How do we follow one business transaction across both systems?
• What happens when the source system changes a field?
• Are the data volumes in the estimate based on our real numbers, or on assumptions?

If two quotes answer these the same way, you can compare them on price. If they don’t, they are quoting for different projects.

Decide early how your systems will connect

Direct, point-to-point connections are the cheapest option for the first two or three integrations. After that they get expensive quickly, because every system ends up depending on every other one. If you expect more than a handful of integrations, a central layer such as an integration platform, an event bus or a well-managed API layer usually pays for itself in the connections you build later.

Many organisations only make this decision after their fourth or fifth direct connection, when changing course costs far more. If you are planning integrations now, we are happy to help you write a brief that vendors can quote on like for like.