What Actually Drives Software Development Costs
The dominant factor is never the technology stack — it is almost always how much is still undecided. Every open question in the brief becomes a contingency inside the number you receive. A vendor that has no visibility into the edge cases must assume the worst. Putting two weeks into requirements work often reduces the final cost much more than any rate negotiation.
Third-party integrations tend to be another reliable source of cost. A form that saves data is easy to estimate; the same feature talking to a legacy ERP is not. The cost hides in the counterparty: poor documentation, waiting on someone else's offshore development team for saudi arabia, data that does not match your model. Ask each bidder to price integrations separately, vue.js vs angular since this is the usual source of overruns.
Quality attributes quietly rewrite the estimate. An internal tool used by twenty people has almost nothing in common with the same feature set serving a hundred thousand users. Security reviews, uptime targets, load handling, traceability and accessibility each add weeks of work. Put them in the brief or you can expect them priced as extras.
Who actually does the work changes the arithmetic. A day rate says very little on its own: an experienced engineer at twice the price frequently turns out to be cheaper overall than a pair of junior developers who need supervision and rework. Check too what else appears on the invoice: delivery management, quality assurance, release engineering and UX design are legitimate costs, but they must be visible in the estimate.
The build price is never the full cost of ownership. Plan for infrastructure, subscriptions and offshore vs nearshore outsourcing licences, monitoring and a maintenance allowance annually. A useful planning figure says that any production system needs a noticeable fraction of its original build cost per year for updates, security patches and small improvements. Leaving it out of the budget remains the classic mistake.