The biggest software development cost driver is not the technology stack — it remains uncertainty. Each unanswered question in the requirements turns into a buffer somewhere in the quote. A vendor that does not know what happens on the unhappy path has to assume the worst. Investing a few days in a discovery phase can cut the overall figure much more than negotiating the rate.

Connections to other systems tend to be the next major multiplier. A form that saves data is predictable; the same feature connected to an old accounting system is another matter entirely. The unknown sits in the counterparty: undocumented APIs, long certification processes, fields that mean something different on each side. Ask any vendor to list every external system, since that is where the numbers slip.

Non-functional requirements can easily double the number. An internal tool used by a small internal team costs far less than the same feature set handling thousands of external customers. Compliance work, uptime targets, load handling, data retention rules and localisation add real engineering time. Put them in the brief or you can expect them priced as extras.

Who actually does the work matters. An hourly rate tells you very little on its own: one senior hire laravel web developer at twice the price frequently turns out to be cheaper overall than two juniors who need supervision and rework. Ask as well which roles are billed: project management, quality assurance, DevOps and UX design are legitimate costs, but these should be visible in the estimate.

The number in the proposal is not what you will actually spend. Expect cloud costs, third-party licences, monitoring and an ongoing support budget each year. A useful planning figure is that any production system requires a recurring percentage of its original build cost annually for updates, security patches and small improvements. Ignoring this remains the most frequent planning error.