£300 for the 128gb is as good as it gets new. They're in big demand so there's absolutely no chance of a sale. There are a lot of scam sites trying to sell them for £95 etc, it's all scams.
2080 should be good enough to drive the q2 reasonably well, depending on the game and the settings.
With Sidequest, you can usually mod the native standalone quest version of beatsaber I believe, though I haven't done it.
As for getting it working with your PC, from everything I've read, every VR headset can be a bit of a faff at times, but the Oculus setup seems to be the most straightforward and least buggy. I've had a bit of fiddlyness with Steam games, but once you get used to the order of loading the softwares up, it's not too bad.
I don't think any games are cross buy in terms of Steam to Oculus etc, but some are in terms of Rift (PCVR) or Quest (Standalone), best to check before buying if that's important to you.
I'd honestly say, if you've got a half decent wireless setup, don't bother with buying a cable straightaway, Airlink is pretty good, and Virtual Desktop (£15 on sale I believe) is also good at providing a wireless PCVR experience.
Quest 2 is great value, there's a good chance you'll want to buy accessories for it though, which can add to the cost, but I'd recommend starting with the headset, and seeing if it works for you. Audio, as a non-audiophile, is just fine for me.
EDIT - Oh, and if you buy through oculus, find a friend who has one already, and get them to give you a referral code, then you both get something like £23 free credit in the store.
