The dominant factor is rarely the technology stack — it is almost always uncertainty. Every ambiguity in the brief turns into a buffer in the estimate. A supplier that does not know the edge cases must assume the worst. Spending a week on a proper discovery can cut the overall figure much more than haggling over hourly rates.
Third-party integrations tend to be another reliable source of cost. A feature that touches only your own data is easy to estimate; the same feature wired into a payment provider and a CRM is not. The cost hides in the third party: undocumented APIs, long certification processes, inconsistent data. Ask each bidder to price integrations separately, since that is where the numbers slip.
The requirements nobody writes down can easily double the budget. A tool used by a handful of staff has almost nothing in common with the same feature set serving thousands of external customers. Audit and compliance requirements, uptime targets, load handling, data retention rules and localisation add real engineering time. Write them down at the start or expect the estimate to move later.
The team you are quoted matters a great deal. An hourly rate says very little on its own: a senior engineer at a premium rate is often cheaper overall than two inexperienced developers who require heavy code review. Also ask which is better vue or angular roles are billed: coordination, quality assurance, DevOps and design are real work, net cloud development but these should be itemised.
The build price is never the full software development cost estimate of ownership. Budget for software development agency hosting, subscriptions and licences, monitoring and a maintenance allowance annually. A useful planning figure is that any production system consumes a meaningful share of the original budget every year for updates, security patches and small improvements. Ignoring this remains the classic mistake.
