Total: 818. would be cheaper if the sapphire 7850 was on stock at newegg, you can buy it off a different site. If you need os, then you are going to have to price cut stuff, coming off of the gpu, and mobo primarily. choices in why i picked in this general area are 2500k gives you overclockign potential(albeit no funds to fit in good cpu cooler, so you cant do any heavy duty one.) and 7850, since it requires 1 6 pin connector, as well as low power consumption to allow you to crossfire if necessary on a 650w psu.
Around $620. Just need a CD/DVD rom, and a 2nd hard drive(s) to store files. You will be able to play any blizzard game on highest settings. You will be able to overclock to 4.5ghz (or close to it). Everything is from Newegg.
Edit: crap forgot the RAM...add $42 for 8gb of GSkill