Hi,
I have lot of experience with Xamarin (Android, Forms, iOS) and also native android apps. I work on daily bases on my primary job. I read you requirements and i would like to check app that you already have. Later after i saw what i need to do we can discuss about time and prize. Also it will be very helpful if you have source from current app.
Looking forward to here from you.
Regards,
Marko.