Lingerie.com has cheap Halloween costumes and right now select styles are 15% off. Choose from a large selection of costumes with the standard "sexy" prefix: Sexy nurse, sexy maid, sexy sailor. The list goes on and on! Plus, all orders get free shipping for a limited time (expiration unknown so shop soon). You could probably recreate the look above with stuff you already have in your closet, too!
Above: Sexy School Girl Costume, now $22.09 at Lingerie.com