A build like this gives you more than enough power for VR...
I wouldn't necessarily say that, as it will depend on the headset. A first-generation Oculus Rift or HTC Vive could likely get along pretty well on an RX 580 due to their relatively low resolution screens, but the newer headsets coming out lately use higher resolution panels, and depending on just how high that resolution is, they would probably want a faster graphics card for it. Especially when you consider that future VR games are likely to become somewhat more demanding.
I would spend more on the graphics card for VR, whether its for a GTX 1660 (about $220 for around 20% more performance), a 1660 Ti (around $280) or a 2060 (around $350). Or maybe one of the upcoming new graphics cards from AMD, depending on when they come out and when the birthday is.
At the very least, it's hard to budget the system without having a better idea of what VR headset they might be interested in. Also, is a monitor going to be required for this system and figured into the cost?