That still seems absurdly crazy, to me, for a frickin' school dance.
You can buy some
amazing memories in college for that sort of cash, and I'm struggling to find an argument that prom would be the most effective use of it. Especially since the description you gave: "Not awful", "not something I particularly enjoyed at the time", doesn't exactly sell the thing,.
(Unless you're, like, that couple who built their outfits out of duck tape. If you do something like that it's probably worth it. :V )
It's kind of one of those 'life events' sort of things that you'd probably regret for the rest of your life if you missed.
it's a large milestone in life. *shrug*
I guess this seems to be the main argument for going bar any other explicit reason (if you have a date you're really into that's really into prom, obviously you wouldn't want to skip it), and to be honest I have no idea what those statements actually mean. So if you're not the kind of person who thinks of your life in terms of culturally determined "milestones" and "events", there's not a whole lot inherent value to the idea.
I'd strongly advise renting a dress over buying one, because 95% of dresses girls get for proms are terrible so never wear them again.
On the other hand, buying a
really nice used dress can often be cheaper than renting! And really, it's just gotta be better than the prom average, how hard can that be?