Upgrade for 2006 rig

I donated a palit 4870 1gb to a friend (coming from a 8800gt). He would like a CPU upgrade since his old dual core can't keep up in games (50$ celerons beat it). ** he's an AMD fanboy and won't buy used**. A phenom 955 would've been great but alas. He still uses this configuration:

Athlon 64 x2 4000+ 2.4 ghz

gigabyte GA-M55S-S3 (rev. 2.0) nforce 550 AM2 motherboard

4x1 GB geil ddr2 ram (dual channel probably)

sirtec high power 500w

It's not much to work with considering a good upgrade would be a complete change of platform including memory but the video card runs well for his needs - a 1600x900 monitor playing newish games but doesn't mind sacrificing details for framerate.

What would be a nice EXTREMELY TIGHT BUDGET upgrade for this PC? An athlon x4 750k would work well with a 4870, which is roughly equivalent to a r7 260 today, enough to run most games on medium/high on 1600x900. Any suggestions are appreciated

Thanks

Man , you're gonna need to upgrade the mobo if you want a new amd cpu .

What's the budjet ? you could get something ok and a bit futureproof with ~160 $ , like a quad core and am3+ motherboard .

The problem is a 8320 with the cheapest 970 chipset motherboard (asrock 970 pro 3) is 272$ in Romania (not the cheapest shop but you get the idea) while in newegg it's 220$. With a 2x4 gb kingston hyperx kit it's 393 here and 309 on newegg...

So with very small budget like you said 160$ am3+ is out of the question because he won't afford at least 4gb ddr3. I'm not sure how much of a difference a 750k vs a more expensive FX 4300 or 6300 will make with his video card. Something decent for 130$ on newegg would work, I don't know the first thing about amd chipsets and I'm not sure which motherboard is good enough.

no used huh... on a 8 year old system... and an extremely tight budget... and DDR2 is extremely expensive now...  I think he is shit up a creek without a paddle. upgrading is basically wasting money.

what is this extremely tight budget, give us a number. Like $174?

http://pcpartpicker.com/p/N7NBhM

If that is too much, just drop the ram and get the CPU. For any kind of significant upgrade, I would recommend a quadcore.

if he still has his hhd and it runs on sata and a 500w power supply this might work.

http://pcpartpicker.com/p/X476qs