Cross-Platform Productivity App Development

I need an experienced mobile app developer to create a cross-platform productivity application for both iOS and Android.

Key Requirements:
- Build a high-performance, user-friendly mobile application
- Design an intuitive UI/UX
- Ensure robust security and data privacy
- Implement offline functionality

Ideal Skills and Experience:
- Proven experience in developing mobile applications for iOS and Android
- Strong knowledge of UI/UX design principles
- Familiarity with security protocols and data encryption
- Experience with offline data synchronization techniques

Please provide examples of previous work, and a detailed project timeline and budget breakdown.