Honestly, find the cheapest iPad you can.
Android is a total crapshoot for bluetooth and ANT+ support, especially on the cheaper/lower end. Tablet android is an additional crapshoot for bluetooth support as well. The nightmare of the clusterfuck that is OEM Android, combined with carrier compromises, combined with odd hardware model compromises means you never know what you will get Android device to device or update to update.
There are numerous threads here about Android bluetooth issues. You can have it working and the next software update totally breaks it (i.e Android 7.0 to 7.0.1, completely broke bluetooth for most, 8.0 and 9.0 have had similar issues with software releases).
The basic 9.7" iPad is a steal for what it is. If it’s still too much you can find refurbished ones or slightly older ones around or under $200’ishUSD online. There are rumblings of new low priced iPad minis being released in the coming months.
iOS 10+ (they are on 12 now and 13 is coming out this year) is bulletproof bluetooth support. You will have many years of trouble free TR use (more if you buy a new iPad) if you spend a little more now.