Well, Halloween is tomorrow and you still have nothing to wear. Have no fear, Lady Gray is here! Actually this next idea came from a Cheap Challenge post by Refinery29 last Halloween, but its brilliance should really be recognized. What is something you can almost guarantee every girl has in her house? Or at least her neighbor's house? Dry cleaning.
This costume is as simple as putting on whatever dress you'd like and then throwing your dry cleaning bag and hanger on over it. Bonus points for making a dry cleaning slip to go with it, stapled onto the bag. Even if you've already taken your dry cleaning out of the bag and thrown away those wire hangers, you can still DIY this costume with minimal purchases that can easily be found at your corner store. Just take a hanger (preferably wire), paper, and markers to make the signature "We <3 Our Customers" hanger, and a clear plastic garbage bag with holes for your arms. Voila! An adorable, clever costume all set to go in just 15 minutes.
If you have some extra time and want to get creative, use wire to create a hanger headband, like the Rent the Runway version above, or add other clothes on hangers to your front and back, like in the Refinery29 version. Now seriously, you only have one day to do this so you better get started.