Ours was $60 back in the '80's because our student body government decided we were going to literally rent a mansion on an island to host the event. Today, that $60 would probably translate to around $180 for each ticket. I wasn't too happy about the high price of admission either, but I came up with it. They have you over a barrel.
Then you should ask your Student Government to explain the cost, as they are the ones who put on the Prom.
The Proms at my high school have always been free to students. The cost has always been covered by fundraising events and boosters/alumni.
If you are having it off capmus there is the cost of the hall rental. Rental of chairs and tables. Entertainment, refreshements. Decorartions. It all adds up quick. My tickets were $20 and with inflation that comes out about to what you are paying.
Ours was only £20 ($30) but it covered the cost of the food, venue, photographer, DJ, lighting, decorations, ect. I think £40 ($60) is quite reasonable for what you're getting out of it.
Thats what the ticket is, its how they get the money to host the event. Thats what it goes towards.
It's probably a fancy prom.