The dominant factor is not the technology stack — it remains uncertainty. Each unanswered question in the requirements is converted into padding inside the number you receive. A vendor that cannot see the edge cases will assume a pessimistic case. Spending a week on a proper discovery often reduces the final cost far more than any rate negotiation.
Connections to other systems tend to be the second big multiplier. A form that saves data is easy to estimate; the same functionality wired into an old accounting system is another matter entirely. The cost hides in the counterparty: poor documentation, long certification processes, data that does not match your model. Ask any vendor to price integrations separately, since this is where estimates break.
Non-functional requirements quietly rewrite the number. A tool used by twenty people costs far less than the same idea handling a hundred thousand livewire development company users. Security reviews, fastify vs laravel availability guarantees, load handling, igaming backend platform audit logging and accessibility add weeks of work. Put them in the brief or you can expect them to arrive later as change requests.
The mix of people behind the number matters. An hourly rate reveals almost nothing on its own: an experienced engineer at a higher rate can be less expensive in the end than a pair of junior developers who require constant review. Also ask what else appears on the invoice: project management, QA, infrastructure work and analysis are real work, but these should be itemised.
The number in the proposal is never what you will actually spend. Budget for hosting, subscriptions and licences, monitoring and an ongoing support budget each year. A reasonable rule of thumb says that any production system consumes a meaningful share of its original build cost per year for updates, azure software development company security patches and small improvements. Leaving it out of the budget has always been the most frequent planning error.