You can get the Cheapest i5 ( about $190) . That's already Quad Core 3.4 Ghz I think. I got mine even cheaper ( $180) i5 3330 at 3.0 Ghz Quad core. and a Generic Mobo for $50. You can even use your existing RAM.
And so this is basically the big debate: FX 6300 or i5 3350P. With the 6300 he could overclock, which he definitely would, but at stock the i5 will be better.
Which would be better? Probably the most CPU intensive game he plays is StarCraft 2.
Ask him Is he Gonna over clock if he is. He can save some $$ with the amd 6300 and still get a blazing cpu. If hes not gonna overclock just go for the i5
My 6300 at 4.5ghz chews games apart. Even somthing like skyrim very cpu intensive I play that game Fully maxed out with max render distance With No lower than a min of 50fps. The 6300 is a great chip for the price. However the i5 is amazing too. Skyrim/battlefield 3/farcry uses all my 6 cores too Oo