Comprehensive Multi-Vendor School Management System Acquisition

I am looking to purchase an existing multi-vendor school management system with the following capabilities:

Essential Functionalities:
- Student management
- Teacher management
- Class scheduling
- Feeding management
- Payment integration
- Non-teaching staff management
- SMS notifications
- Newsletter distribution
- Online/offline library management
- PTA management

The system should support both online and offline library management.

Ideal candidates should have:
- Experience with school management systems
- Proven track record in system integration, especially payment systems
- Ability to provide a demo or trial of the system
- Strong support and maintenance post-purchase

Please provide any relevant experience, system architecture details, and a clear cost breakdown.