The dominant factor is not the technology stack — it is almost always how much is still undecided. Every open question in the brief turns into padding somewhere in the quote. A vendor rust erp that has no visibility into what happens on the unhappy path has to assume the worst. Putting two weeks into a discovery phase often reduces the overall figure by 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 predictable; the same functionality talking to a payment provider and a CRM is a different problem. The effort hides in the counterparty: undocumented APIs, slow approval cycles, inconsistent data. Ask the estimator to list every external system, as this is the usual source of overruns.
Non-functional requirements can easily double the estimate. A tool used by a small internal team costs far less than the same idea serving public traffic. Audit and compliance requirements, high availability, scalability, hire angular audit experts logging and accessibility all add weeks of work. Write them down at the start or expect them priced as extras.
Who actually does the work matters a great deal. A rate card tells you very little on its own: one senior developer at twice the price can be less expensive in the end than a pair of junior developers who require supervision difference between vue and angular rework. Also ask what else appears on the invoice: project management, quality assurance, DevOps difference between livewire and react UX design have to be done by someone, but they must be named rather than hidden inside a blended rate.
The number in the proposal is rarely the total cost. Budget for infrastructure, paid APIs, logging and alerting and an ongoing support budget each year. A reasonable rule of thumb says that software in active use needs a recurring percentage of the original budget every year in fixes, updates and small changes. Leaving it out of the budget has always been the most frequent planning error.