Why there is no honest universal price
Two systems with the same number of screens can have completely different costs. Identity, permissions, integrations, data migration, offline behavior, audit needs and the quality of an existing codebase change both effort and risk. A useful estimate names those variables instead of hiding them inside one attractive number.
Scope the decision, not the wish list
Begin with the user, the operational constraint and the smallest complete journey that changes the outcome. Acceptance criteria should describe observable behavior. Features that do not affect the first decision can move to a later option, keeping the initial investment tied to learning or operational value.
Budget for verification and ownership
Implementation without tests, deployment preparation, documentation or observability may look cheaper because cost was postponed. Ask what code, access, environments and handoff material the buyer receives. Also separate the estimate for building from third-party subscriptions, cloud consumption and ongoing product evolution.
Compare proposals on assumptions
A strong proposal explains unknowns, exclusions, dependencies and how changes will be handled. Compare whether each supplier understood the same workflow and risk. The cheapest fixed figure can become the most expensive option when it relies on assumptions the operation cannot satisfy.