The quad core is more than enough, i loaded wow up on a old Celeron with on board graphics, with a usb with draenor and was able to play on low but smoothly, but point is while the game can be cpu intense, lately its more gpu intense and at some points actually gets my 7970 up to 85% use on ultra 1080p, no steadily but peak.
You can get a fairly cheap card to play high/ultra such as the 750 ti if ur psu isnt a good one, or you can get a used gtx 670 for around the price of the 750ti and same with some 7970s off ebay or the forums deals section, but prob more towards 150+. My friend just sold his gtx 760 for $150, and i recently bought a 7770 for $40 used of course.