Dear client. How are you?
I am extremely experienced in iOS and Android app development with 5 years and I am also very strong at server back-end programming, as well as synchronizing app and MySQL database by developing and integrating JSON-RESTful server API modules.
In my opinion, I think we must use the MERN to build this app, because it supports both android and iOS at the same time, so that can do save your money and time.
Based on analysis of your requirement and from my experience, I offer $8000 / 60 days.
Milestone steps:
1st - front end development based on provided app design.
2nd - back end completion.
3rd - Admin panel completion
4th - Integration of front end and back end.
Of course, my offer is a bit higher than other freelancer's bid, but when you think about the high-quality product for your successful business, I think it's a correct time and reasonable budget.
I will do my best in order to realize your ideas into reality.
Please contact me, I hope to discuss this job in more detail.
Regards.