The biggest cost driver is rarely the technology consulting company stack — it is how much is still undecided. Every ambiguity in the brief becomes a buffer inside the number you receive. A vendor that does not know the exceptions and edge cases must assume the worst. Putting two weeks into requirements work often reduces the overall figure by far more than haggling over hourly rates.
Integrations tend to be the second big multiplier. A form that saves data is easy to estimate; the same functionality wired into a payment provider and a CRM is not. The effort lives in the counterparty: rate limits and sandbox access, slow approval cycles, data that does not match your model. Ask each bidder to fixed price software development integrations separately, as this is the usual source of overruns.
The requirements nobody writes down silently change the budget. A tool used by a small internal team costs far less than the same idea handling a hundred thousand users. Security reviews, availability guarantees, load handling, data retention rules and igaming software multi-language support add weeks of work. Put them in the brief or else expect them to arrive later as change requests.
Who actually does the work matters a great deal. A rate card reveals very little on its own: an experienced engineer at a higher rate frequently turns out to be less expensive in the end than two juniors who require supervision and rework. Check too what else appears on the invoice: project management, testing, release engineering and design are real work, but they should be itemised.
The quoted figure is never the total cost. Plan for cloud costs, third-party licences, outsource python development observability and a maintenance allowance for every year the software runs. A reasonable rule of thumb holds that software in active use needs a noticeable fraction of the original budget per year in fixes, updates and small changes. Leaving it out of the budget has always been the most common budgeting mistake.