The dominant factor is rarely the technology stack — it outsourcing company remains uncertainty. Every open question in the brief is converted into a buffer somewhere in the quote. A team that does not know the exceptions and edge cases will assume the worst. Spending a week on requirements work can cut the total much more than any rate negotiation.
Integrations remain the next major multiplier. A feature that touches only your own data is predictable; the same feature wired into a payment provider and a CRM is a different problem. The cost hides in the third party: poor documentation, long certification processes, fields that mean something different on each side. Ask each bidder to list every external system, as this is where estimates break.
The requirements nobody writes down silently change the number. A tool used by a small internal team has almost nothing in common with the same functionality serving a hundred thousand users. Audit and compliance requirements, availability guarantees, scalability, traceability and multi-language support add weeks of work. Put them in the brief or else expect them to arrive later as change requests.
The mix of people behind the number changes the arithmetic. A rate card reveals almost nothing on its own: one senior developer at a premium rate frequently turns out to be less expensive in the end than a pair of junior developers who need constant review. Check too what else appears on the invoice: project management, quality assurance, release engineering and UX design are legitimate costs, but these should be named rather than hidden inside a blended rate.
The quoted figure is never the total cost. Budget for cloud costs, vue.js vs angular subscriptions and licences, observability and a maintenance allowance annually. A common working assumption says that a live system consumes a noticeable fraction of the initial investment annually in fixes, web development company updates and small changes. Ignoring this is the most frequent planning error.