The biggest cost driver is not the technology stack — it remains how much is still undecided. Each unanswered question in the specification is converted into a contingency inside the number you receive. A team that cannot see what happens on the unhappy path must assume the worst. Investing a few days in requirements work often reduces the total much more than negotiating the rate.
Integrations are the next major multiplier. A screen that writes to your own database is low risk; the same feature talking to a legacy ERP is not. The cost sits in the third party: undocumented APIs, slow approval cycles, data that does not match your model. Ask the estimator to list every external system, as this is where estimates break.
The requirements nobody writes down can easily double the estimate. A tool used by twenty people is a very different build from the same functionality handling a hundred thousand users. Compliance work, uptime targets, performance under load, audit logging and localisation each add real engineering time and materials vs fixed price contract. Put them in the brief or nearshore software development you can expect the estimate to move later.
The mix of people behind the number matters. A day rate says very little on its own: one senior developer at a premium rate is often cheaper overall than two inexperienced developers who require supervision and vue js developer for hire rework. Check too which roles are billed: project management, quality assurance, release engineering and analysis have to be done by someone, but they must be visible in the estimate.
The build price is rarely the total cost. Plan for hosting, third-party licences, logging and alerting and a maintenance allowance annually. A common working assumption is that a live system needs a meaningful share of the initial investment every year for updates, security patches and small improvements. Leaving it out of the budget has always been the most frequent planning error.