Thanks a lot for all the replies people

Gladly enough my parents won't stop supporting me if I don't go (I don't even think they would if I'd go in tux), so if I have to choose between 'dress' and 'don't go' I know what I'll do.
But yeah, my friends are there too, and actually I WANT to go, but NOT in a DRESS. I have been in a dress, with makeup, high heels, the 'full deal', once and that was once too many! (I got myself into it by friends saying "you'll like it when it's done" and me thinking "mmm, okayyy... can't judge when you don't try")
Another difficulty is the price. I don't think my parents will pay anything (bad financial weather over here), but it seems impossible to rent a tux for 50 e or less (preferably not above 40 e, but that's probably impossible, lol)
Gladly they haven't already bought a dress, they were just looking for stuff and calling out "oohh, see this! You like this one?" (and if I said "no" (with every dress) they got angry because "I was being a grump" *facepalm*)
*sigh* I think I'll just not go... but I'd love to come proudly in a tux V__V That would just be awesome and badass!