I wanted to post pics but their site wouldn't let me right click...If you're going for cheap, what about Forever21? Especially since you said you're a stick, they tend to run petite.
I think a basic black dress is always in good style. Call me old fashioned (but not old, I AM only 28) but I feel like for an occasion like this it's always chic and in style. Plus they come in a good price range, the one at forever 21 was only 29 and really cute. I got mine a few years ago at Dillards on clearance for only 14$ and I have worn it many many times. With a basic black dress you can wear nice jewlery or maybe a scarf and really look great without killing your budget.
I would go with black, or some other solid color, cocktail dress (knee length). It's what they were invented for. I quite like the green J.Crew dress posted above...you get the idea.
Hybrid Mode
