What I usually do is go to ebay and see what prices the others sale their parts as individuals. For example your gpu is being sold around 80-150 euro on ebay depending its version (HIS,Gigabyte etc). I think the 350 is a good price to start.
the video card is the most prized possession in the case. the cpu is extremely outdated. my thoughts, even $300 would be a lot. and that's if the operating system disc goes with it. sell it for 200/250 U.S. dollars. keep your friendship. buy your new machine. what you paid for it doesn't matter.