your LBS is a great place to pick up a cog. surly, dura ace, whatever... they can probably get it for you. they are only $15 or so, so if you got a "deal" online you might get it for $10... support the LBS!
and i agree about 8am classes not being *that* bad... i think it's the not going to bed until 2-3am that kills it, and only having it 2 days a week instead of every day. throws my sleep pattern off.