The biggest cost driver is never the choice of framework — it is almost always uncertainty. Every open question in the specification is converted into padding somewhere in the quote. A supplier that cannot see the edge cases will assume the more expensive option. Putting two weeks into a discovery phase can cut the overall figure by far more than any rate negotiation.
Connections to other systems remain the second big multiplier. A screen that writes to your own database is low risk; the same feature wired into a payment provider and ai chatbot development company a CRM is another matter entirely. The unknown hides in the other system: rate limits and sandbox access, long certification processes, fields that mean something different on each side. Ask the estimator to price integrations separately, since this is the usual source of overruns.
The requirements nobody writes down can easily double the estimate. An internal tool used by a handful of staff has almost nothing in common with the same feature set handling a hundred thousand users. Audit and compliance requirements, uptime targets, load handling, traceability and localisation add weeks of work. Put them in the brief or expect them to arrive later as change requests.
Who actually does the work matters a great deal. A day rate reveals almost nothing on its own: one senior edtech software development developer at twice the price can be cheaper per delivered feature than a pair of junior developers who need supervision and rework. Ask as well what else appears on the invoice: project management, hire php unit testing engineer quality assurance, infrastructure work and UX design have to be done by someone, but they should be named rather than hidden inside a blended rate.
The build price is not the full cost of ownership. Expect cloud costs, third-party licences, observability and a change budget each year. A useful planning figure is that software in active use requires a recurring percentage of the initial investment every year in fixes, updates and small changes. Leaving it out of the budget is the most common budgeting mistake.