The biggest cost driver is rarely the technology stack — it is how much is still undecided. Every open question in the brief turns into a contingency inside the number you receive. A vendor that does not know what happens on the unhappy path must assume the worst. Investing a few days in requirements work can cut the overall figure by far more than negotiating the rate.
Integrations remain the next major multiplier. A screen that writes to your own database is low risk; the same screen wired into a legacy ERP is another matter entirely. The effort lives in the third party: rate limits and igaming platform development sandbox access, slow approval cycles, data that does not match your model. Ask each bidder to price integrations separately, because this is where estimates break.
Non-functional requirements silently change the number. An internal tool used by a handful of staff has almost nothing in common with the same feature set handling a hundred thousand users. Security reviews, high availability, load handling, data retention rules and multi-language support all add weeks of work. Put them in the brief or you can expect them to arrive later as change requests.
The team you are quoted changes the arithmetic. A day rate tells you little on its own: an experienced engineer at a higher rate frequently turns out to be cheaper overall than two juniors who need constant review. Also ask who else is billed: software development for regulated industries delivery management, QA, DevOps and analysis are real work, hire vue developers but they must be named rather than hidden inside a blended rate.
The quoted figure is not the total cost. Budget for hosting, third-party licences, observability and custom retail ecommerce software development a change budget each year. A common working assumption says that any production system needs a meaningful share of the original budget per year simply to stay current. Ignoring this is the most frequent planning error.