Sadie hawkins dance...tickets???

ok at my high school we r having a sadie hawkins semi formal dance the tickets r $10 in advance or $15 at the door... me and my friend r both going w/ our bfs... but knowing them they will probably forget that we have 2 get tickets and all that jazz... sooooooo wat is the proper ettiqute anyway... do the girls buy the tickets since we asked??? do the guys buy the ticket since they r the guy??? or do we each buy our own???and wat about a corsauge??? do u need those 4 semi-formals???