You can get a phenom II 945 these days for <100 bucks. They are not unlocked, but can be easily overclocked to 3.3 on stock voltages, and 3.6 with a good cooler. They are hard to come by now that they are all snatched up. If you toss in another 10 bucks or so, you can get a 965BE that is unlocked:http://www.ncix.com/products/index.php?sku=46281&vpn=HDZ965FBGMBOX&manufacture=AMD&promoid=1261
But if your board doesn't support DDR3, the performance gain will be limited. Although you can always upgrade board later on.