The dominant factor is never technology — it remains uncertainty. Every open question in the specification becomes padding in the estimate. A team that cannot see what happens on the unhappy path has to assume the worst. Putting two weeks into a proper discovery can cut the final cost much more than negotiating the rate.
Connections to other systems tend to be the second big multiplier. A form that saves data is low risk; the same screen wired into a legacy ERP is another matter entirely. The cost hides in the third party: undocumented APIs, waiting on someone else's dedicated team model, inconsistent data. Ask any vendor ai development agency to price integrations separately, because that is where the numbers slip.
Non-functional requirements can easily double the budget. A tool used by twenty people is a very different build from the same feature set handling a hundred thousand best react js development company users. Security reviews, availability guarantees, load handling, audit logging and accessibility each add measurable effort. Write them down at the start or you can expect them priced as extras.
The mix of people behind the number changes the arithmetic. A rate card tells you very little on its own: nearshore outsourcing one senior developer at a higher rate is often cheaper per delivered feature than two juniors who require constant review. Ask as well which roles are billed: project management, quality assurance, infrastructure work and design are real work, but they should be itemised.
The quoted figure is never the full cost of ownership. Plan for infrastructure, subscriptions and licences, monitoring and an ongoing support budget for every year the software runs. A useful planning figure holds that any production system needs a noticeable fraction of the initial investment every year simply to stay current. Leaving it out of the budget remains the most frequent planning error.