For consumer PC VR, $600 is probably too low.
However, for Unity VR development right now with an Oculus Rift DK2, you might be able to have a decent experience with something similar to:
CPU
Intel Core i3-4160 3.6GHz Dual-Core Processor
$109.99
Motherboard
Gigabyte GA-H81M-H Micro ATX LGA1150 Motherboard
$43.98
Memory
Kingston 4GB (1 x 4GB) DDR3-1600 Memory
$31.74
Storage
Crucial MX100 128GB 2.5" Solid State Drive
$64.95
Video Card
EVGA GeForce GTX 960 2GB Video Card
$196.98
Case
Rosewill FBM-01 MicroATX Mini Tower Case
$29.99
Power Supply
Corsair CX 600W 80+ Bronze Certified Semi-Modular ATX Power Supply
$47.50
Total: $525.13
Price doesn't include OS, keyboard, mouse, monitor, and HMD.
I'm on a similar spec machine with AMD FX 3.4 GHz and a GeForce 760. I mostly consume my own content, and sometimes content from Oculus Share. While performance isn't the best, it isn't terrible either and I get 75+ fps in many demos.