You can shop around for logic boards on ebay or something, but I've had success using a heat gun to reflow the solder. Some say to bake it in the oven, but the heat gun method is easier and more accurate IMO.
There are also places that will repair it with new solder that doesn't melt and crack like the stock junk did causing the issue in the first place. I'd have to go look for them now, but I think it was like $200-300 plus shipping.
In the end though, it may be easier to cut your losses and purchase a newer MBP. I had a 2007 model that was working perfectly fine and sold it just in case, and went to a 2010 model. Good speed boost and it came out around the same price it would be to fix the other one in the first place.