gotta go ebay ... theres lots of cpu's there for around 50 bucks .
look for socket A or socket 462
Dont buy a sempron (you have been warned) even though they go to 3300-3400 + there actually slower then a 2400+ tbred ....(yes SkyChimp the sempron socket A suks IMRO)
your best bet is either a 2400+ tbred , 2500+ ,2600+ ,or 3200+ barton
the 2500+ mobile barton is overclockers delight of the bunch (what i run still)but its also in the be cautious when buying used as for its the laptop cpu and some have been overheated .
the KV7 can run any of those cpu's . I'm not shure if it can run a sempron though (the older 462 amd boards need the bios flashed to run the slower POS semprons ) the kv7's Via chipset is ok and that mainboard clocks nicely .