[Alumiyum]

Forever21, Charlotte Russe, and Urban Outfitters usually have cute party dresses at low prices. Also try lulus.com. The prices vary, but you can get really original dresses at still reasonable prices.

He should pay since he invited you, but it wouldn't be out line to ask, especially if he's a good friend. Just say you want to make sure he knows you can do your part if you need to, which isn't outright asking and also isn't outright offering to pay.

Whenever me or my sisters went to fraternity formals with guys that were just friends we asked to room together and the guys always agreed to it, so the girls could share a bed. I've stayed in the same bed with a guy friend before, but it was a large one and we were both long time friends, so it wasn't a problem. If you don't know him all that well I'd definitely try to stay with a girlfriend or just tell him beforehand that you just want to set the record straight...if he's a good guy he'll offer to take the floor or couch or find a girl for you to stay with. Not every guy assumes they'll get booty from a formal date...but every now and then you run into a bad egg.