Extra money? You mean, for mobo replacement... Well, your best shot for LGA775 is Core 2 Quad Q9650. If you're willing to pay a lot, Core 2 Extreme QX9650 or QX9770 (they're slower than most of the new Core i series, but cost way more).
Keep your LGA 775 around for a bit more, then get next generation Intel stuff like Ivy Bridge, if it'll be good.
Check crags list, here in Seattle Washington people are selling there entire core 2 quad core extreme edition systems for $350' and that's about the same as the CPU u are looking at, if you can get a hold of one, scrap the computer and take the CPU. And sell the remaining parts from the computers on craigslist to make some money back, ppl are always looking for stuff, good luck.