prom party wears specially designed for seventeen

I am in need of a formal dress for a special event in September. Full length or cocktail is fine. Not sure I want to spend the $$ to buy one as I don't have many formal events in my life prom party wears specially designed for seventeen :)
Anyone out there have a dress I could borrow? Size 2-4 or XS/S depending on cut.
Or suggestions for where to shop for one? LOL

Looking for Recommendations