Budget-Friendly Marketplace App

I’d like to launch a lean, cross-platform marketplace where people can buy and sell products straight from their phones. The app must ship on both iOS and Android in the same release cycle, so using a shared codebase (Flutter, React Native or similar) will help us stay within my tight budget... (Budget: $1500 - $3000 CAD, Jobs: Android, Flutter, iOS Development, iPhone, Mobile App Development, Payment Gateway Integration, PHP, React Native)