Yes, you can do it yourself. You would have to open the Mac, so you will void your warranty. I did it with mine, worked great.
Not too hard to do if you are good with your hands. You can buy the card
here or look for it on Ebay. Its retail price is $49.95, but they have been jacking the price everywhere. Supply and Demand. I got lucky and found it at the Compusa they were closing around me. They had it for $20 bucks
Instructions on how to can be found
here.
Good Luck, feel free to PM with any questions.