Hi Zoe:
Thanks for visiting the Disney Parks Moms Panel. I love dining at Cinderella's Royal Table, I am positive you will have a wonderful experience with your daughter. Many princesses do dress up for the occasion, so I think a new princess dress for your daughter is a great idea. I do find that the princess dresses available at Walt Disney World Resort are slightly more expensive compared to the dresses available at the Disney Store, however, I also feel that that quality of the dresses are better at Walt Disney World Resort as well. The dresses available at Walt Disney World have more details (sparkles, ruffles, lace etc.), and I find the fabrics to be higher quality. The dresses available at Walt Disney World Resort are also exclusive to the Theme Parks, meaning they are only available for purchase at the theme parks, nowhere else. I love shopping on Main Street U.S.A. for my daughter's princess attire, however, her favourite spot is the shop
Castle Couture behind Cinderella Castle. She likes this shop as the Cast Members are always available to sprinkle some Pixie Dust on little princesses and princes.
If you are worried about the cost, I would suggest that you purchase a dress prior to your arrival, just to make sure your princess has a dress for the occasion.
I hope that helps Zoe. Please let me know if you have any other questions as your vacation approaches. I would be happy to help.
Stephanie