Cross-Platform Productivity App Development

I need a complete mobile solution—a productivity-focused app that runs smoothly on both iOS and Android. I already have the core concept mapped out; what’s missing is the design, coding, and store-ready packaging... (Budget: $30 - $250 AUD, Jobs: Android, Appcelerator Titanium, Flutter, iPhone, Mobile App Development, React Native, UI / User Interface, UX / User Experience)