Dress Up America on Amazon are selling these gorgeous dress up items for the insanely low price of £3.26 and up. They are all add-on items, so you have to spend over £10 to get them sent out, but that works out to just over three outfits. The stock levels on this are dropping like crazy though, so you'll have to be quick. I just tried to buy the Strawberry Shortcake style outfit in my daughter's size and the price in my basket showed up at over £12 rather than the £3.26 it was when I added it to the basket, and is now out of stock, so do act quickly.
Even those items that aren't almost 90% off have good prices - like 47% off, makes the Strawberry girl costume £12.93, and it's a pretty decent dress up outfit!
Each outift has a variety of children's or adult size options, and each option has it's own price, so it's a bit of hit and miss, but they do have exquisite costumes.