I need a dress for prom something y evening and bright?

i am willing to pay about $400 to $500 for a dress or less but something that looks well made not cheap and one of a kind at least me being the only one wearing it i like bright colors that compliment me like deep purple or red please help me i have been looking but have come up witht the same old same ol i also like designer labels if that helps ohh and i kinda have a big but and bust i wear a 6 but with an 8 for alterations thanks