No. No. NO!
HandyAndy is right. The guy DOES have to pay for the girl, unless your school is free. You don't have to pay for the dress though...thats WBAFC...borderline milk-toast
Prom itself is a very romanticized, idealized, pseudo-"party-date"
Do you know why it becomes a huge popularity contest between females, and (quite pathetically) it is often the highlight of a stupid high school broad's lifetime?
The whole thing is constructed around putting the girl, the prom-date, on a pedestal. The girls put on the best looking dress they will ever wear in their entire life with the exception of them being a model or a wedding dress, they spend literally hours making themselves look great, all to get their male prom date to be a "gentleman."
This sh(i)t would be perfect! ....if we were in the 1600s....Blame feminism.
With that being said, alot of guys are LJBFriended the moment they step into the prom venue. Most guys at my school take girls they are just "friends" with anyways.
Thus the whole idea of "prom" is AFC. When guys ask girls to prom, unless they've been in a relationship beforehand (and this often isn't the case..at least from my experience). You naturally become slotted as an AFC anyways going to prom.
It doesn't mean you can escalate. You can release your inner-DJ and bypass the initial AFC parts of prom. (Thats how a few guys get "lucky" during prom).
Also, this doesn't mean you can't have fun with a girl at prom of course. If possible though, find some way to make her pay for her own way in, even though its against the "etiquette"