iOS/Android Gym Booking App

I need a complete mobile application that lets users reserve gym time by the hour and pay instantly on their phones. The same code-base (or two native builds if you prefer) must run smoothly on both iOS and Android, matching Apple and Google design guidelines... (Budget: $250 - $750 USD, Jobs: Android, Android App Development, App Store Optimization, iOS Development, iPhone, Mobile App Development, Payment Processing, PHP)