Here are demos of the VR performance of a $400 VR-capable PC proving that you can build a cheap pc for oculus rift or htc vive with a GTX 1050Ti 4GB (with Intel i5-4590 and 8GB). Pls. note this video is at 24fps but the actual gameplay is 90fps.
More info here: http://360rumors.com/2017/04/best-desktop-vr-system-q1-2017-plus-demos-400-vr-capable-pc.html
Here is how I put together the $400 Oculus-ready PC: https://www.youtube.com/watch?v=0eIZpGKhPgY
Yes, you can get roomscale VR with 2 sensors. Here’s how: http://360rumors.com/2016/12/tutorial-how-to-use-the-oculus-rift-and-touch-for-roomscale-vr-with-just-two-sensors.html
Roomscale according to Valve’s definition is 2m x 1.5m: “For room-scale setup, a minimum play area of 2 m x 1.5 m (6 ft 6 in x 5 ft) is required.”