The dominant factor is never the choice of framework — it remains unclear scope. Every open question in the specification turns into padding inside the number you receive. A vendor that has no visibility into what happens on the unhappy path will assume the more expensive option. Investing a few days in a proper discovery often reduces the final cost much more than any rate negotiation.
Connections to other systems tend to be another reliable source of cost. A form that saves data is predictable; the same screen wired into a legacy ERP is a different problem. The unknown lives in the third party: poor documentation, slow approval cycles, fields that mean something different on each side. Ask each bidder to price integrations separately, as this is the usual source of overruns.
Quality attributes can easily double the estimate. An internal tool used by a handful of staff costs far less than the same functionality handling a hundred thousand best node js development company users. Audit and compliance requirements, high availability, scalability, traceability and localisation add weeks of work. Write them down at the start or expect the estimate to move later.
The team you are quoted changes the arithmetic. An hourly rate reveals very little on its own: an experienced engineer at a premium rate frequently turns out to be less expensive in the end than two juniors who need supervision and rework. Also ask which roles are billed: coordination, testing, DevOps and UX design are real work, but they must be named rather than hidden inside a blended rate.
The quoted figure is never the full cost of ownership. Expect cloud costs, paid APIs, monitoring and an ongoing support budget for every year the software maintenance and support services runs. A reasonable rule of thumb is that software in active use requires a noticeable fraction of its original build cost per year in fixes, updates and small changes. Ignoring this has always been the classic mistake.