If you are sold on the Disney one only, my hope is that you stumble upon a sale. However, if you are simply looking for a snow white dress you might try etsy.com. This is a site where people post handmade items for sale. I purchased a gorgeous belle dress for my daughter for our recent trip. It was made by uniquebizaar and was beautifully made. I paid only $75 for the dress, tiarra, earrings, bracelet, necklace, gloves, and hoop skirt.The designer was even willing to make it in pink, my daughter's favorite color for no additional charge. My daughter received so many compliments on this dress and it truly brought tears to my eyes to see her in it. I would do a search for disney princess dresses and see what you find. Some are very reasonably priced while others are way over the top.
Best of luck,
Cris