Costume

I am having a very difficult time deciding what to be for Halloween. I think I have three problems:

I am not rich and therefore am not willing to spend more than $20 on a costume I will probably not wear more than once.

I do not want to wear something that looks cheap, despite the fact that it will be.

I don't know how to sew.

If I could solve any one of these problems by Oct. 29, we'd be in business, because I would still have time to put something together by Halloween. However, I don't see a solution coming. My plan now is to raid my closet to see if some of those dresses I wore to my high school dances and banquets still fit, go to Goodwill to see if they have anything I can butcher into an acceptable costume, and possibly spend a little bit more than $20 if I can find something that I can use with other costumes in the years to come. If you have any other suggestions, they would be greatly appreciated. Thanks!

P.S. What is the point of all those high school dances and banquets? They are fun, I grant you, but does anyone really go to that kind of thing in real life? I have not been to an event requiring a dress/gown like those since I graduated. I would love to attend such an event, but I've never had the opportunity, and certainly not two or three times a year.