[nucleardog]

As more anecdata, I had a pretty satisfactory experience with my Vive on an old R9 290x from ~2013. Some more demanding games would occasionally stutter, but everything was generally smooth (based on the performance graph not dropping below the HMD's refresh rate).

The Index is higher resolution/refresh rate and will require more hardware, but if you just want to get into some VR and dick around, the Vive is more than enough to get started, can be found for <$200 used, and a ton of the popular games (e.g., Beat Saber, SuperHot VR, etc) just really aren't that graphically demanding.

The Vive is also compatible with the knuckles controllers and those can be purchased separately, so you're not totally locked out from some of the more game changing stuff either.