You need a bike and tire on roller trainer a blue tooth cadence and speed sensor, a decent computer, phone or tablet to get started. Before messing with the bike and trainer I would check that zwift runs on your computer and that the screen is a decent size. I had to borrow a laptop and eventually buy a new ipad and hdmi connector.
To be honest by the time you’re done all this the smart trainer won’t seem so expensive
Get a kurt kinetic road machine trainer, if you can find one used they work great and have a lifetime guarantee. You can also use the kurt kinetic inride sensor, which will register as a power meter as opposed to the dreaded “zpower”. This review may help:
Don’t settle with magnetic non-smart trainer, you’ll want to get a fluid trainer at minimum because it gives a “road like” feel, meaning the way it works your muscles is more equivalent to riding outside. You’ll also have a very high max wattage, whereas some trainers cap out at 400 watts, which may sound like a lot now but once you start getting in shape you will realize that it’s not very high.
This trainer by kurt kinetic is what I’m talking about. It says smart-trainer but it really isn’t. Smart trainers automatically change the difficulty depending on the gradient on the zwift course. This is a non-smart wheel on trainer:
You can also purchase this instead of the newer version of the inride if you plan on using bluetooth only since it is not compatible with ant+:
The sensor registers as a power meter in zwift so you won’t need to purchase a separate speed and cadence sensor, which will likely cost as much or more as the kurt kinetic inride sensor.
The other accessory I would get is a wahoo tickr heart rate monitor. I prefer the chest strap since it seems more accurate than the arm band sensor:
Other than that you’ll just need the bike with gears and a trainer tire. I think you should be able to get all of this for $300 or less if you can find a used kurt kinetic trainer.
I have the Kurt Kinetic with the InRide sensor 3 and it is GREAT.
James has given you good advice.
Keep your tires inflated and do a spin down calibration each use (takes 20 secs) and you’re good to go.