The biggest cost driver is rarely the choice of framework — it is unclear scope. Every ambiguity in the specification turns into a buffer in the estimate. A vendor that does not know the exceptions and python development services edge cases will assume the more expensive option. Investing a few days in requirements work can cut the overall figure much more than any rate negotiation.
Third-party integrations remain another reliable source of cost. A form that saves data is low risk; the same screen wired into an old accounting system is a different problem. The cost lives in the other system: poor documentation, waiting on someone else’s team, inconsistent data. Ask the estimator to price integrations separately, because that is where the numbers slip.
Quality attributes silently change the number. An internal tool used by a handful of staff has almost nothing in common with the same functionality handling thousands of external customers. Compliance work, hire memcached developer uptime targets, load handling, traceability and localisation each add real engineering time. Put them in the brief or you can expect the estimate to move later.
The mix of people behind the number matters a great deal. An hourly rate tells you very little on its own: one senior developer at twice the price frequently turns out to be cheaper per delivered feature better than php two inexperienced developers who need constant review. Ask as well who else is billed: delivery management, quality assurance, infrastructure work and UX design are real work, but these should be itemised.
The build price is never the full cost of ownership. Plan for infrastructure, paid APIs, observability and a change budget annually. A reasonable rule of thumb is that a live system requires a meaningful share of its original build cost per year in fixes, updates and small changes. Leaving it out of the budget has always been the most frequent planning error.