I could be wrong, but I bet the difference in price between a 2 piece and a dress is simple supply and demand. They just don't sell nearly as many dresses as they do 2 piece costumes. I majored in fashion merchandising at school, which is really a major in retail. If dresses suddenly became more popular than 2 pieces then the price of 2 pieces would come down and they'd be telling us that the dresses cost more because they entail extra fabric and beading, ya know?