Development Budgeting & Cost Analysis

I'm building a multi-platform price-comparison and bill-switching product (responsive web + native iOS + native Android) for the EU market, launching in Spain first. I'm looking for an experienced, independent fractional CTO to prepare a development budgeting document for the build. Scope of this contract (one-off): Review my product brief / requirements and the existing development-agency proposals I've received. Prepare a realistic budget and cost breakdown to build the product, with clearly stated assumptions. Flag risks, likely hidden costs, and where quotes look inflated or unrealistic. Provide a recommended budget and an honest technical read on the best path forward. Deliverable: a written budgeting document (cost breakdown + assumptions + recommendations).