Nvidia is attempting to standardise minimum requirements for its VR Ready program. A desktop PC needs a Geforce GTX 970, a notebook should run a GTX 980M at least. You'll also need an Intel Core i5-4590 processor, at least 8 GB of RAM, two USB 3.0 ports and a HDMI 1.3 port. On top of that the unit needs to run Win 7 (with Service Pack 1) or newer.
Nvidia has started a labeling system called "VR Ready." In partnership with different PC and component manufacturers, Nvidia is certifying hardware as being "Geforce GTX VR Ready."
Nvidia's partners include Alienware as well as retailers such as Amazon. The "cheapest" possible GPU being the GTX 970 currently sells at around $329.99. Nvidias VR Ready label matches the minimum requirements for the Oculus Rift that Oculus VR laid out last spring.