The GPU is soldered onto the logic board, so the whole logic board has to be replaced. This makes the repair an expensive one, costing a half of the price of the MacBook or more. If it's cheaper, you are lucky, because the logic board is the most expensive part.
Considering this, you may want a new MacBook Pro if the cost is high
I may have someone who *might* be able to do the repair cheaply, so it would just be the part being the main cost...
I'm ordering a new one anyway as it was getting long in the tooth anyway, and as said - selling this was to part fund it. I'm living in hope it might be worthwhile to fix to get the best price for it!
I don't know what it would cost to replace and it's quite possible that there is no longer anyone who replaces it as the part is not made anymore. What most repair people do is called reflowing. This is where they take out the logic board ad wrap it in tin foil, then bake it so the gpu melts into place. This is not permanent but will give you a couple of months. BUT, it is not the only way, and there is a DIY way that can be done for FREE. Here is what you should do:
1. Plug in your macbook pro (make sure that its off)
2. Turn on the computer, and hwen it chimes, close the lid and turn it updside down.
3. Wrap the macbook in a heavy quilt.
4. Let the computer sit for about an hour.
5. Take it out of the quilt, unplug it and let it cool for 20 minutes.
6. Turn on the computer.
Thats all you need to make your macbook pro run for another 4-6 months! I can attest to this as i had the same thing and i am typing this on that very computer. IT IS NOT PERMANENT, but it CAN be repeated as many times as you want, s you could keep it goin for another 2 years or so.