The biggest cost driver is not the technology stack — it is unclear scope. Each unanswered question in the brief turns into padding in the estimate. A team that has no visibility into the edge cases has to assume the more expensive option. Putting two weeks into requirements work frequently cuts the final cost far more than haggling over hourly rates.
Third-party integrations remain the next major multiplier. A feature that touches only your own data is easy to estimate; the same feature wired into a legacy ERP is not. The effort hides in the other system: rate limits and sandbox access, nextjs development agency long certification processes, data that does not match your model. Ask any vendor to price integrations separately, because this is where estimates break.
Non-functional requirements can easily double the number. An internal tool used by a handful of staff is a very different build from the same feature set serving public traffic. Audit and compliance requirements, availability guarantees, scalability, audit logging and angular development company multi-language support all add weeks of work. Write them down at the start or you can expect the estimate to move later.
Who actually does the work matters a great deal. A day rate tells you almost nothing on its own: an experienced engineer at a premium rate is often cheaper per delivered feature than two juniors who need heavy code review. Check too who else is billed: project management, testing, release engineering and design are real work, but they should be named rather than hidden inside a blended rate.
The number in the proposal is never the full cost of ownership. Plan for infrastructure, subscriptions and licences, monitoring and an ongoing support budget for every year the software runs. A useful planning figure holds that software in active use needs a recurring percentage of its original build cost per year simply to stay current. Ignoring this is the most frequent planning error.