The dominant factor is rarely the choice of framework — it remains uncertainty. Each unanswered question in the specification is converted into padding inside the number you receive. A vendor that has no visibility into the edge cases has to assume the worst. Investing a few days in a discovery phase can cut the total far more than haggling over hourly rates.
Connections to other systems remain another reliable source of cost. A feature that touches only your own data is easy to estimate; the same functionality talking to a payment provider and a CRM is not. The cost hides in the third party: poor documentation, vue.js vs react long certification processes, inconsistent data. Ask each bidder to price integrations separately, as that is where the numbers slip.
The requirements nobody writes down silently change the estimate. An internal tool used by a handful of staff costs far less than the same idea handling thousands of external customers. Audit and compliance requirements, uptime targets, load handling, audit logging and multi-language support each add measurable effort. State them early or you can expect them to arrive later as change requests.
The team you are quoted matters. An hourly rate reveals almost nothing on its own: an experienced engineer at a premium rate frequently turns out to be cheaper overall than two inexperienced developers who need supervision and rework. Check too which roles are billed: delivery management, testing, release engineering and UX design have to be done by someone, but they should be named rather than hidden inside a blended rate.
The quoted figure is never what you will actually spend. Plan for real estate platform development company infrastructure, paid APIs, logging and alerting and an ongoing support budget for every year the software development company decision guide runs. A reasonable rule of thumb is that any production system requires a noticeable fraction of the original budget per year in fixes, updates and small changes. Treating the launch as the finish line has always been the most common budgeting mistake.