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The dominant factor is not the technology stack — it is how much is still undecided. Every open question in the brief turns into padding inside the number you receive. A vendor that cannot see what happens on the unhappy path must assume a pessimistic case. Investing a few days in a discovery phase often reduces the overall figure far more than haggling over hourly rates.
Connections to other systems are the next major multiplier. A screen that writes to your own database is low risk; the same feature wired into a legacy ERP is not. The effort sits in the counterparty: vue js vs reactjs poor documentation, long certification processes, fields that mean something different on each side. Ask any vendor to list every external system, react native consulting services because this is where estimates break.
Non-functional requirements can easily double the budget. An application used by a small internal team costs far less than the same feature set handling thousands of external customers. Audit and react js development services compliance requirements, high availability, performance under load, traceability and multi-language support each add weeks of work. Write them down at the start or you can expect them to arrive later as change requests.
The team you are quoted changes the arithmetic. An hourly rate says almost nothing on its own: python vs php performance a senior engineer at a premium rate frequently turns out to be cheaper per delivered feature than a pair of junior developers who require constant review. Check too which roles are billed: delivery management, testing, infrastructure work and analysis are real work, but they should be named rather than hidden inside a blended rate.
The build price is never what you will actually spend. Expect cloud costs, paid APIs, observability and an ongoing support budget for every year the software runs. A useful planning figure holds that any production system requires a noticeable fraction of the original budget every year simply to stay current. Leaving it out of the budget is the most common budgeting mistake.