Bidding will close about 1 hour before the run starts, at which point Brossentia will purchase the selected costume. Any availiable costume for LittleBigPlanet 1 can be selected. We've pre-entered Brossentia's recommended choices.
Other choices can be found here: http://www.littlebigplanet.com/en/game_guide/ps3/downloadable_content/ and here: http://littlebigplanet.wikia.com/wiki/Downloadable_Content