well with the amd athlon 250, i would say getting a gtx 770 is out of the question.
so the only course he can take is upgrading his cpu, now this very much depends on his motherboard. you can find this out by (assuming your on windows) start search dxdiag and hit enter
its most likely however his mobo is am3 only which means he is going to be very limited to upgrading his cpu.
its also worth noting AMD's sockets are very versatile its again very unlucky the next gen of CPU's from them will support any current motherboard he can buy on that budget.
Dont worry there is light out of this tunnel.
Wow is a very old game, and thanks to amd there are cpu solutions that will enable him to game and keep under budget.
i would recommend a Richland APU in this particular scenario. make sure if he does consider this the mhz of his ram is very important. (along with what the mobo can support)
this should keep him under the budget with room to upgrade in the future.
hope this helps.