The biggest cost driver is rarely technology — it is almost always uncertainty. Every ambiguity in the requirements turns into a contingency in the estimate. A vendor that does not know what happens on the unhappy path has to assume the more expensive option. Investing a few days in a proper discovery often reduces the overall figure far more than negotiating the rate.
Integrations remain the second big multiplier. A feature that touches only your own data is easy to estimate; the same screen wired into an old accounting system is a different problem. The cost sits in the third party: rate limits and sandbox access, slow approval cycles, inconsistent data. Ask the estimator to break integrations out as separate items, which is better flutter or react native since this is the usual source of overruns.
Non-functional requirements silently change the number. A tool used by twenty people costs far less than the same feature set serving thousands of external customers. Security reviews, availability guarantees, performance under load, audit logging and localisation add weeks of work. Write them down at the start or react native development company you can expect them to arrive later as change requests.
Who actually does the work changes the arithmetic. A day rate tells you very little on its own: one senior developer at a higher rate frequently turns out to be less expensive in the end than two juniors who require constant review. Ask as well which roles are billed: project management, testing, release engineering and UX design have to be done by someone, but these should be itemised.
The quoted figure is not the full cost of ownership. Budget for ai chatbot development company cloud costs, subscriptions and licences, observability and a maintenance allowance each year. A useful planning figure is that any production system consumes a noticeable fraction of the original budget per year simply to stay current. Leaving it out of the budget is the most frequent planning error.