I've been searching for the dressing up costume with the dress (not the stylin' Stephaine one with the wig and handbag), and I've found one in stock on a US site. It costs $24.99 for the costume and a further $29.95 for shipping but this works out at a total of just £28 GBP! which, if you've seen the ebay prices you'll know is a bargain.
Here's the site here .