The GPU market is really bad right now with short supply directly from the factories and another mining boom that is taking place, it has caused a giant domino effect as a whole and even just entry level gaming cards are picked dried in many places, causing older cards that aren't suitable for VR to go up in price as well.
If you're just after starting VR and messing around, there are quite some old cards that in theory supports it, you could on some games make do with an old 970 from Nvidia(obviously not recommended today). It's a bit a matter of what you aim for and money you wish to spend. But if you're serious about VR and you're team AMD, I wouldn't be recommending anything below a 5700 or 5700XT if you could find one used for a decent price, and unless you need one right here and now, you might be better off waiting and see when the 6700/6700xt becomes available if you can get one.
I myself played some VR using a vive headset on my 1070ti and it did just fine in the few titles I tried, so you don't really need anything amazing if you just want to pick up VR and play today. I know a lot of people have success with things like 1060(6GB ver) from nvidia in the likes of HL alyx, but it struggles a bit on the highest settings. In general it's a big "all depends".
Since the prices are a bit jacked up right now everything will be a bit more expensive and it might not come down in a while if we're unlucky, maybe a bit more stable prices back again after Summer.
