Ill write numbers what to upgrade first to last
CPU- i5 3570 (k for OCing) 3
mobo- p8b75 (z77 for OCing) 3
PSU- corsair cx600 (for future upgrades) 2
GPU- HD 7770 (7850 or 660 if you get higher budget later on) 1
ram- 2*4 Gb crucial ballistiX tactical 1600MHz 5
OS- windows 7 home premium 64bit 4
This all costs more than 200 bucks but you can all of them in future.