Everyone's favorite band now in pun form! Just glue a few nickels onto an old undershirt and you've got one of the most creative costumes at the party (mostly because of the Nickelback jokes) and it literally costs a few cents!
Fluffy and Harry
This one takes a bit of work, but if you just take 2 stuffed animal dogs and throw the heads on your own pooch you have Fluffy from everyone's favorite Harry Potter! Seriously, will Harry Potter ever get old?
Maybe not your best bet if you're going out for a night of bar hopping (I doubt a large knife would be allowed most public places), but if you're just crashing a friend's party then "Cereal Killer" is unique and SUPER easy to pull off.
50 Shades of Grey
Grab some paint samples from your local Home Depot and a couple finger paints and you have this hilarious costume. Just make sure that you actually pick 50, you know there will be that 1 friend who actually counts.