To get the best experience on Zwift, I recommend you save money on the bike and spend it on a Smart Trainer.
If you buy a cheap, second-hand real bike and pair it with a Smart Trainer (instead of buying cadence, speed or power sensors) you create your own “smart bike” which can give you the full Zwift experience.
By “full Zwift experience”, I mean that the right smart trainer takes data from Zwift and changes resistance automatically to simulate going up and down hill.
For me, that’s a fundamental part of enjoying Zwift. Any old bike can work; it just needs working gears and a way to drive the trainer via a chain or wheel.
Here’s a great resource to check out: