I would try it yourself. I have bought 6+ for £20 off ebay repaired them and then sold them to friends for a slight profit. They know what was the matter with them before I repaired them. Out of the 6 I can count in my head. Only 1 has done it again. All I done was repeated the procedure and It's still going strong.
some tips I have picked up:-
Buy yourself some very good quality thermal paste and alcohol wipes (to remove the old paste).

Use a proper heat gun (Not a hair dryer).

Be very methodical in taking the screws out and line them up so you know the correct order for re-assembly.

Have a digital camera to take snaps of where you took Screws/plugs/ribbons out.

I know the procedure off by heart now. Just don't forget to plug the cmos battery back in! It's one of the last things to come off the board before you re flow it and if you don't plug it back in it won't work!

The key is to getting the right amount of thermal paste on the chips and getting the best quality paste you can find. I have used cheap paste on one of my own before and it didn't last 20 minutes.

Give it a go and if your stuck I'm only a pm away