Easy last-minute Halloween costumes

Astronaut—Search local thrift stores for a mothballed NASA space suit. Be sure to avoid Skylab era suits, as their automatic orientation systems (AOS) may be leaking radioactive Cesium. Aside from being a serious health risk, it leaves a stain that makes it look like you peed yourself in orbit.
Price: $53,000-$57,000 based on condition
Prep time: none

Wall Street Big Shot—Take a large, sharp spoon and hollow out a Wall Street big shot. Don hide. Due to spoilage issues, costume works best in cold weather. 
Price: $0.00, not including legal defense
Prep time: Couple hours

Ghost—Throw an old white bed sheet over yourself. Don’t forget to cut out a mouth hole so you can drink at Halloween parties. If you’re driving, you may wish to consider cutting out eye holes as well. Variation: use a fitted sheet if you are going as a mentally disabled ghost.
Price: $0.00
Prep time: 10-15 minutes if going with eye hole option

Princess—Go to a fabric store and pick up several yards each of tulle, taffeta, satin and velvet, plus a princess gown pattern. Drop these off with the royal seamstress while you go tiara shopping. By the time you return, your gown should be ready for first fitting. Once necessary alterations are made, dress in gown, top with tiara.
Price: Approx. $137,000, depending on quality of fabric and total carat weight of tiara
Prep time: 1 glorious afternoon

Dude—Where what you have on. Practice saying, “Dude, I’m not into costumes and shit. I just came to party.”
Price: $0.00
Prep time: Depends on how long it takes you to memorize your line

Windmill—Continuously flail your arms.
Price: $0.00, not including shoulder surgery
Prep time: none