The single largest cost driver is rarely the choice of framework — it is how much is still undecided. Every ambiguity in the specification is converted into a buffer in the estimate. A team that does not know what happens on the unhappy path has to assume the worst. Putting two weeks into a proper discovery often reduces the final cost much more than negotiating the rate.
Connections to other systems tend to be another reliable source of cost. A screen that writes to your own database is predictable; the same screen talking to a payment provider and a CRM is not. The effort hides in the third party: rate limits and sandbox access, waiting on someone else’s team, data that does not match your model. Ask any vendor to break integrations out as separate items, because this is where estimates break.
Quality attributes can easily double the number. An internal tool used by twenty people has almost nothing in common with the same functionality serving a hundred thousand react native development company users. Audit and compliance requirements, uptime targets, performance under load, audit logging and multi-language support add measurable effort. State them early or expect them to arrive later as change requests.
The team you are quoted matters. A day rate says almost nothing on its own: a senior engineer at a higher rate frequently turns out to be cheaper overall than two juniors who require supervision and rework. Ask as well who else is billed: coordination, quality assurance, release engineering and analysis are real work, top node.js development companies but they should be visible in the estimate.
The build price is rarely the total cost. Budget for cloud costs, subscriptions and licences, monitoring and an ongoing support budget each year. A reasonable rule of thumb holds that software in active use requires a noticeable fraction of its original build cost every year in fixes, updates and small changes. Ignoring this has always been the most common budgeting mistake.