Agencies quote ranges because the range is real. Here is what moves the number.
Platform count is the biggest lever, then backend complexity, then compliance. A single-platform MVP with a hosted backend and no regulated data lands far below a two-store release with offline sync and an audit trail. Everything else — animation polish, a design system, a second language — is a rounding error by comparison.
The estimator on our homepage runs the same model we quote from internally. It will not be exact, but it will be honest, and the two-week scoping sprint turns the range into one figure you can take to a board.