iBuypower AM690 is a VR-ready PC for $749, with free Amazon Prime shipping. It comes with a VR-ready AMD RX480 graphics card.
- Intel Core i5-6402P Quad Core 2.8GHz Processor (3.4GHz with Turbo) | B150M Chipset
- AMD RX-480 8GB graphics card
- 8GB DDR4 Memory
- 1TB 7200RPM HDD
- USB 3.0 x 2 and USB 2.0 x 4.
- 802.11ac Wireless Adapter
- Windows 10 Home
- iBUYPOWER Gaming Keyboard and Mouse
Please note that the Oculus Rift requires three USB 3.0 ports (possibly four with the Oculus Touch), so you'll have to add a USB 3.0 card to the AM690 if you want to use the Rift. The HTC Vive uses one USB 2.0 port.
The AM690 is similar in price and specs as the CyberPowerPC Gamer Xtreme VR ($720), except that the AM690's graphics card has 8GB of RAM while the Xtreme VR's card has 4GB of RAM. On the other hand, the AM690 has only two USB 3.0 ports, while the Xtreme VR has six USB 3.0 ports.
You can buy the AM690 from Amazon here. Update: it's seems to be currently out of stock. Back in stock in 1 to 3 months.