Which VR hardware to purchase for PC?

First up, the hew HL has the minimum spec declared as a GeForce GTX 1060 -- and the Oculus Rift will nag you in the menus if you're using less than a GTX 980, so you'll be wanting to upgrade your GPU too.

If you're not fully committed to VR, a second hand Oculus Rift or HTC Vive (the two "first generation" headsets) is the cheapest way in :)
The Oculus Quest can be used standalone or with a PC now ("Oculus Link") - if mobile VR interests you, then that model is ideal mixture.

WindowsMR headsets are ok, but less polished than the HTC/Oculus/Valve offerings. I'd consider them if you can find one at a good price and that's your goal (low price). The HTC/Oculus/Valve ones are pretty much equally good, IMHO.

If you want the full HL:Alyx experience, it's going to be optimized 100% for the Valve Index... which also has the fancy "knuckles" controllers.

IMO the RTX 2070 is the current sweet spot for VR. But if it's really just about playing HL in 2020, you could find a stopgap upgrade on eBay (should be plenty of 980s and 1070s) and buy something big later.

Promit said:
IMO the RTX 2070 is the current sweet spot for VR

Worth mentioning that if you don't specifically care about the RTX features, you can often find a similarly-performing GTX 1080 on sale for half the price of the 2070 (I picked up an EVGA B-stock 1080 for under $300 a while back).