The dominant factor is never the technology stack — it remains how much is still undecided. Every open question in the brief is converted into padding somewhere in the quote. A team that has no visibility into what happens on the unhappy path must assume the more expensive option. Putting two weeks into requirements work often reduces the final cost far more than negotiating the rate.

Third-party integrations are the next major multiplier. A screen that writes to your own database is low risk; the same feature wired into a payment provider and a CRM is a different problem. The unknown lives in the counterparty: poor documentation, long certification processes, data that does not match your model. Ask each bidder to list every external system, since this is where estimates break.

The requirements nobody writes down silently change the estimate. An application used by a handful of staff has almost nothing in common with the same feature set serving public traffic. Compliance work, high availability, performance under load, audit logging and localisation each add real estate software development services engineering time. Write them down at the start or you can expect the estimate to move later.

The mix of people behind the number changes the arithmetic. A rate card tells you very little on its own: an experienced engineer at a premium rate can be less expensive in the end than a pair of junior angular developers for hire who need supervision and rework. Also ask who else is billed: coordination, testing, release engineering and design have to be done by someone, but they should be named rather than hidden inside a blended rate.

The build price is rarely what you will actually spend. Expect infrastructure, subscriptions and licences, observability and an ongoing support budget annually. A common working assumption is that software in active use requires a recurring percentage of its original build cost every year for updates, security patches and small improvements. Leaving it out of the budget is the classic mistake.