Build Cross Platform Mobile App

I need a complete mobile application that runs smoothly on both iOS and Android. While the final concept is still open, I know I want a professionally coded app that is ready for the App Store and Google Play, with thoughtful UI/UX and clean, maintainable source code included... (Budget: ₹1500 - ₹12500 INR, Jobs: Android, Flutter, HTML5, iOS Development, iPhone, Mobile App Development, React Native, UI / User Interface)