Costume contest prize ideas?

We are having a costume party later this month and I'm trying to figure out what to do as a prize for the best costume (everyone will vote for best costume).

I was just thinking about buying something, but my husband suggested having everyone who want to participate in the contest bring a $5-10 gift card to enter, and then the winner gets all the gift cards.

What do you think? Would you bring a gift card to participate in the contest for a chance to win all of them? My husband and I wouldn't be participating, but we would add gift cards as well, just in case not many people participate.

Or would you rather just participate for free and have the chance of receiving an item? If so, what kind of items?