Under $100, closer to $60 and under.
Forever 21, Stitches, Urban Planet, Le Chateau. I actually bought one of my dresses at Le Chateau, $40, I loved it. Look around Macy's even and shop the sales, you'd be surprised what you can find sometimes. Don't be afraid to look in smaller stores out of the malls on the streets, or even a thrift store.
Buffalo Exchange! If there's one near you. It's a mid-range resale shop; not as expensive as the high-end ones Marisha mentioned (where a "cheap" designer dress will still likely run over your budget), but lots more current fashions than you'll find at, say, a Goodwill.
If you have a high end resale shop in your area you could find a very expensive designer dress for next to nothing in cost....And likely worn once and noone will know you didn't pay anywhere near full price for it.
im not a girl and im not sure where you live if you have one but platos closet? my sister goes there all the time for cheap dresses(there used but still nice only worn a few times
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DEB! they have super cheap ones! I got my homecoming dress at Forever 21 for $24. There's also Charlotte Russe.
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Agaci. I love getting dresses their.