>>371108917
The absolute cheapest would be something like a quest with a kinect or something but that would be terrible. You could get an old vive and htc trackers but at this point vives are increasingly hard to find and outdated enough that its not really sensible to buy one
You can run a hybrid setup with a quest hmd and htc trackers but this is less than ideal and if you are buying the base stations anyway honestly just get an index
The index is still the king of vr it really has no major weak points except arguably the cable
If you buy anything else you will eventually either just buy an index (or whatever is better) or drop vr entirely
People have used all sorts of setups over the years and almost everyone just grabs an index+htc trackers eventually, maybe tundras will become the new standard but theyre still unavailable to buy unless you kickstarted