The single largest cost driver is rarely technology — it remains unclear scope. Every open question in the brief turns into a buffer somewhere in the quote. A supplier that has no visibility into the edge cases must assume the worst. Putting two weeks into a discovery phase can cut the total far more than haggling over hourly rates.
Connections to other systems tend to be another reliable source of cost. A form that saves data is predictable; the same screen wired into a payment provider and app aso agency a CRM is a different problem. The unknown lives in the third party: undocumented APIs, slow approval cycles, fields that mean something different on each side. Ask the estimator to price integrations separately, as this is where estimates break.
The requirements nobody writes down can easily double the number. An internal tool used by a small internal team has almost nothing in common with the same functionality serving public traffic. Compliance work, uptime targets, performance under load, audit logging and accessibility all add measurable effort. State them early or you can expect the estimate to move later.
Who actually does the work matters. A day rate tells you very little on its own: a senior engineer at a premium rate can be less expensive in the end to end project development than a pair of junior developers who require supervision and rework. Also ask which roles are billed: project management, testing, infrastructure work and 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. Budget for infrastructure, subscriptions and licences, logging and alerting and a change budget annually. A useful planning figure says that real estate software development company in active use needs a meaningful share of its original build cost every year for updates, security patches and small improvements. Leaving it out of the budget remains the classic mistake.