The single largest cost driver is not the technology stack — it remains how much is still undecided. Every ambiguity in the brief turns into a buffer in the estimate. A supplier that cannot see the exceptions and edge cases must assume a pessimistic case. Investing a few days in requirements work often reduces the final cost far more than haggling over hourly rates.
Third-party integrations tend to be the next major multiplier. A form that saves data is low risk; the same screen wired into a legacy ERP is another matter entirely. The unknown sits in the third party: react development company undocumented APIs, waiting on someone else’s team, data that does not match your model. Ask each bidder to break integrations out as separate items, since that is where the numbers slip.
Quality attributes quietly rewrite the estimate. An internal tool used by a small internal team has almost nothing in common with the same idea serving a hundred thousand users. Compliance work, availability guarantees, load handling, traceability and multi-language support add weeks of work. State them early or expect the estimate to move later.
The mix of people behind the number changes the arithmetic. A rate card says almost nothing on its own: one senior developer at twice the price frequently turns out to be cheaper per delivered feature than a pair of junior developers who require constant review. Also ask what else appears on the invoice: delivery management, quality assurance, release engineering and russia software development agency analysis have to be done by someone, but they must be itemised.
The number in the proposal is never the full cost of ownership. Expect infrastructure, subscriptions and licences, observability and an ongoing support budget annually. A reasonable rule of thumb says that any production system consumes a meaningful share of the original budget every year simply to stay current. Treating the launch as the finish line has always been the classic mistake.