The single largest cost driver is rarely the technology stack — it is uncertainty. Every open question in the brief turns into a buffer inside the number you receive. A vendor that does not know the edge cases has to assume the more expensive option. Spending a week on a proper discovery can cut the total far more than any rate negotiation.
Integrations are the next major multiplier. A form that saves data is low risk; the same functionality connected to a payment provider and a CRM is not. The unknown sits in the counterparty: rate limits and sandbox access, slow approval cycles, data that does not match your model. Ask any vendor to price integrations separately, since that is where the numbers slip.
Quality attributes quietly rewrite the estimate. An application used by twenty people is a very different build from the same functionality handling a hundred thousand users. Compliance work, high availability, performance under load, traceability and multi-language support add real engineering time. Put them in the brief or you can expect the estimate to move later.
The team you are quoted changes the arithmetic. An hourly rate reveals very little on its own: an experienced engineer at twice the price can be cheaper overall than a pair of junior developers who need supervision and rework. Ask as well who else is billed: coordination, QA, release engineering and UX design are legitimate costs, but they should be named rather than hidden inside a blended rate.
The build price is not what you will actually spend. Expect hosting, subscriptions and licences, monitoring and an ongoing support budget for every year the turnkey software development services runs. A reasonable rule of thumb is that software development company in qatar in active use requires a noticeable fraction of the original budget every year simply to stay current. Leaving it out of the budget has always been the most common budgeting mistake.