I am hoping you can help with my determining a fair price for a 2002 Gary Fisher Marlin. My older son owned the bike until 2005 and when he upgraded bikes, a friend of mine bought it from him. She attempted mountain biking and it was not something she enjoyed, so the bike was infrequently ridden. She asked if I wanted to buy the bike back for my younger son. It appears to be in very good condition. Any ideas as to a fair "buy back" price?