You will need a full computer with at least a GTX 970 (or an AMD r9 290) and at least an i5-4950 (or maybe an AMD FX 8350). Here's [1] a good guide, but roughly $800 for just the machine.
Then you need keyboard, mouse, monitor, internet, power...
Then you need Windows 10 (roughly $100).
Then you need games, which you will probably get through Steam [2] or through Oculus [3].
That's on top of the ~ $600 for an Oculus Rift, or ~ $800 for an HTC Vive.