I see this question has been asked numerous times and I’m still not seeing an answer that makes sense to me -
What do you need in terms of a rear cassette for the bike to fit on the hub one without too much fiddling?
US - Indianapolis, prefer less than $200 but I don’t have to be super strict on that.
The answer is 8
https://support.zwift.com/zwift-hub-bike-compatibility-SJb5xCVgs
there’s some 16 speed bikes here for 399 USD:
A 7 speed bike will work as well, as long as the rear dropouts are 130mm or 135mm spacing. You may need to put an 8 speed chain on it, but that will work fine and it’s a good idea to go with a new chain anyway.
If you’re still shopping for the trainer, consider this: