Obviously wouldn't be a lot, but seeing as it's a fully functional laptop it would be crap not to get *anything* for it. It's a bit slow and the fan runs hot and gets a bit noisy, but other than that it's fine. Changed the keyboard once, and the screen after the other one was smashed. Put in some extra ram at some point as well.
How much do you think would be a realistic amount to ask for?
I can get my hands on a 1 year old Pro for a pretty nice price, you see – but being constantly broke, I still need some cash from somewhere.