The biggest cost driver is not the choice of framework — it is unclear scope. Every ambiguity in the requirements is converted into a contingency inside the number you receive. A supplier that does not know the edge cases will assume a pessimistic case. Investing a few days in requirements work frequently cuts the overall figure much more than haggling over hourly rates.

Integrations remain the next major multiplier. A screen that writes to your own database is predictable; the same feature wired into a payment provider and a CRM is not. The cost hides in the third party: poor documentation, waiting on someone else's hire dedicated development team, fields that mean something different on each side. Ask any vendor to break integrations out as separate items, as this is the usual source of overruns.

The requirements nobody writes down quietly rewrite the budget. An internal tool used by a handful of staff has almost nothing in common with the same idea serving a hundred thousand users. Security reviews, uptime targets, performance under load, traceability and accessibility add measurable effort. State them early or you can expect the estimate to move later.

The mix of people behind the number matters. An hourly rate reveals little on its own: one senior developer at a premium rate can be cheaper overall than two inexperienced developers who need constant review. Check too which roles are billed: delivery management, hire edtech developers testing, infrastructure work and design are real work, but they should be visible in the estimate.

The number in the proposal is never the full cost of ownership. Expect cloud costs, paid APIs, monitoring and an ongoing support budget each year. A common working assumption holds that software in active use consumes a noticeable fraction of the initial investment annually for updates, security patches and small improvements. Treating the launch as the finish line remains the classic mistake.