The main cost drivers
Product complexity, user roles, integrations, compliance, data migration and performance targets have the greatest effect on delivery effort.
A discovery phase reduces uncertainty by translating business requirements into validated workflows, architecture decisions and a prioritized roadmap.
Budget by delivery stage
Plan separately for discovery, product design, engineering, quality assurance, launch and ongoing improvement. This exposes hidden costs and makes trade-offs easier.
A smaller, measurable first release is usually safer than building every planned capability before collecting real user evidence.
How to request a reliable estimate
Provide your business goal, users, critical workflows, current systems, deadline constraints and success metrics. Ask vendors to state assumptions, exclusions and technical risks.