disneyshopping.com often has great deals on costumes. (And everything else.) Check the outlet to see if they have anything first. They change the costumes every 6 months or so, so the older style (which is usually very similar to the newer style) is on clearance. Even for the new costumes, they often have great sales - a few days ago they had a 29% off sale sitewide. They have some sort of new deal going on every day, so just keep checking the site, or do a search for "disney shopping coupons."