Instead of buying a typical costume from a Halloween shop, try making your own. It's a guarantee that no one else will have it. Here are some of my favorite DIY costumes that I've come across.
This is probably my favorite! Can work as a birthday present or any other type of gift bag.
Turn yourself into pop art.
Rosie the Riveter
I've NEVER seen this one done before - Jellyfish!
LikeWowLala on YouTube has a pretty good DIY Miley costume video.
Bunch of Grapes - wear solid color top and stick bunches of balloons on.