The single largest cost driver is rarely the technology stack — it is how much is still undecided. Every open question in the specification turns into padding somewhere in the quote. A team that cannot see what happens on the unhappy path must assume a pessimistic case. Spending a week on requirements work frequently cuts the total by far more than negotiating the rate.
Third-party integrations are the next major multiplier. A feature that touches only your own data is easy to estimate; the same functionality wired into a payment provider and a CRM is not. The cost lives 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, as that is where the numbers slip.
The requirements nobody writes down can easily double the number. A tool used by twenty people is a very different build from the same feature set serving a hundred thousand users. Compliance work, availability guarantees, scalability, audit logging and outsource react native development localisation all add measurable effort. Write them down at the start or else expect them to arrive later as change requests.
The mix of people behind the number changes the arithmetic. A day rate tells you almost nothing on its own: global software development company an experienced engineer at twice the price is often less expensive in the end than two inexperienced developers who require heavy code review. Check too what else appears on the invoice: coordination, testing, release engineering and design have to be done by someone, but these should be visible in the estimate.
The quoted figure is not what you will actually spend. Plan for hosting, third-party licences, monitoring and an ongoing support budget annually. A useful planning figure holds that software in active use requires a recurring percentage of its original build cost annually in fixes, updates and small changes. Leaving it out of the budget has always been the most common budgeting mistake.
