There is a huge black market in Adderall at my college but, to the best of my knowledge, none in Modafinil.
Probably because Adrafinil is still unscheduled and essentially the same thing, nobody really is that worried about paying a premium for modafinil. I've been buying adrafinil for a little over 2 dollars per dose. Modafinil is better for everyday use (more liver stress with adrafinil) especially if you can get a scrip, but "study aids" are normally not taken every day anyway.
Modafinil is now being covered by at least one insurance company in Massachusetts under which it costs less than $1 for a 200 MG pill. I predict a huge college black-market trade in the drug.