The dominant factor is never the technology stack — it is uncertainty. Every open question in the brief turns into a contingency in the estimate. A supplier that does not know what happens on the unhappy path will assume the worst. Investing a few days in requirements work often reduces the total much more than haggling over hourly rates.

Integrations tend to be another reliable source of cost. A form that saves data is low risk; the same feature wired into a legacy ERP is another matter entirely. The effort sits in the other system: undocumented APIs, waiting on someone else's team, fields that mean something different on each side. Ask any vendor to break integrations out as separate items, because that is where the numbers slip.

The requirements nobody writes down can easily double the number. An application used by a small internal team is a very different build from the same idea serving a hundred thousand users. Audit and compliance requirements, availability guarantees, scalability, traceability and multi-language support each add weeks of work. Put them in the brief or you can expect the estimate to move later.

The team you are quoted matters. A day rate says almost nothing on its own: an experienced engineer at twice the price can be cheaper per delivered feature than two inexperienced developers who require supervision and offshore vs nearshore outsourcing rework. Also ask which roles are billed: coordination, quality assurance, DevOps and hire edtech developers analysis have to be done by someone, but they should be visible in the estimate.

The quoted figure is not the full cost of ownership. Expect infrastructure, subscriptions and licences, monitoring and a change budget annually. A reasonable rule of thumb is that software in active use requires a meaningful share of its original build cost per year for updates, security patches and python versus php small improvements. Ignoring this is the most common budgeting mistake.