You might as well be buying a loose hu card. The rest of it is worthless/useless. If the front and back of the hu card were perfect then maybe I'd offer him $60, but the back is terrible. I could live with it though. $40 would be a good offer, $50 is pushing it in my eyes.
If you do buy it, the first thing I'd do is clean the back of the hu card with more goo gone until all the silkscreening was removed. Then I'd bust out a scanner, scan any TurboChip, clean it up in Photoshop, and either have a sticker made or actually get some silk and emulsion and silkscreen it again. Make sure to use Nylon ink with the bonding agent mixed in. It's just a default print on the back.