The dominant factor is never technology — it remains unclear scope. Every ambiguity in the specification turns into a contingency somewhere in the quote. A team that cannot see what happens on the unhappy path has to assume a pessimistic case. Spending a week on requirements work often reduces the final cost much more than negotiating the rate.
Integrations are the next major multiplier. A screen that writes to your own database is predictable; the same functionality wired into a legacy ERP is another matter entirely. The effort sits in the counterparty: poor documentation, waiting on someone else’s team, data that does not match your model. Ask the estimator to break integrations out as separate items, because this is where estimates break.
Non-functional requirements can easily double the number. An internal tool used by a handful of staff is a very different build from the same idea serving public traffic. Security reviews, high availability, scalability, traceability and multi-language support each add real engineering time. Write them down at the start or react js development outsourcing expect them to arrive later as change requests.
The team you are quoted changes the arithmetic. A rate card says very little on its own: one senior flutter developer for hire at twice the price is often cheaper per delivered feature than two juniors who need constant review. Ask as well what else appears on the invoice: project management, quality assurance, infrastructure work difference between laravel and symfony analysis are legitimate costs, but they should be named rather than hidden inside a blended rate.
The number in the proposal is never the full cost of ownership. Plan for hosting, third-party licences, logging and alerting and a change budget annually. A useful planning figure says that software in active use needs a noticeable fraction of its original build cost every year simply to stay current. Treating the launch as the finish line is the most frequent planning error.