The dominant factor is not the choice of framework — it remains unclear scope. Every open question in the specification is converted into padding inside the number you receive. A supplier that does not know what happens on the unhappy path must assume the worst. Putting two weeks into requirements work often reduces the total far more than negotiating the rate.
Third-party integrations remain another reliable source of cost. A form that saves data is predictable; the same screen talking to a payment provider and a CRM is not. The cost sits in the counterparty: rate limits and sandbox access, long certification processes, inconsistent data. Ask each bidder to list every external system, because this is the usual source of overruns.
Non-functional requirements can easily double the budget. An internal tool used by twenty people is a very different build from the same idea handling thousands of external customers. Compliance work, high availability, performance under load, audit logging and localisation all add real engineering time. Put them in the brief or else expect the estimate to move later.
The mix of people behind the number changes the arithmetic. A day rate tells you very little on its own: one senior developer at a higher rate is often less expensive in the end than a pair of junior developers who need constant review. Also ask what else appears on the invoice: coordination, edtech web application hosting QA, infrastructure work and UX design are legitimate costs, but these should be visible in the estimate.
The quoted figure is never the full cost of ownership. Plan web application development for edtech cloud costs, subscriptions and licences, monitoring and a maintenance allowance each year. A reasonable rule of thumb says that a live rag system development with langchain needs a recurring percentage of the original budget per year simply to stay current. Ignoring this is the classic mistake.
