The biggest cost driver is not technology — it is almost always uncertainty. Every open question in the specification is converted into a contingency inside the number you receive. A supplier that has no visibility into the exceptions and staff augmentation company edge cases will assume the more expensive option. Putting two weeks into a discovery phase often reduces the overall figure by far more than haggling over hourly rates.
Third-party integrations tend to be another reliable source of cost. A form that saves data is low risk; the same screen talking to an old accounting system is not. The cost sits in the third party: ai in software outsourcing undocumented APIs, typescript api framework long certification processes, inconsistent data. Ask each bidder to list every external system, since this is where estimates break.
Quality attributes silently change the number. A tool used by a small internal team is a very different build from the same idea serving thousands of external customers. Audit and compliance requirements, high availability, scalability, crypto futures trading software development traceability and localisation add measurable effort. State them early or expect the estimate to move later.
The mix of people behind the number changes the arithmetic. An hourly rate reveals almost nothing on its own: a senior engineer at a higher rate is often cheaper per delivered feature than two juniors who require heavy code review. Also ask who else is billed: project management, testing, DevOps and design are legitimate costs, but they must be named rather than hidden inside a blended rate.
The quoted figure is not the full cost of ownership. Budget for infrastructure, paid APIs, observability and a change budget each year. A common working assumption is that a live system needs a noticeable fraction of the original budget per year in fixes, updates and small changes. Leaving it out of the budget remains the most common budgeting mistake.