I think I found it for you! Super cute, organic, fair trade, festive, and only $48!
Party Dress from One Mango Tree
(also available in black, and check out their other cute clothing as well!)
One Mango Tree uses a fair trade model to provide income generating opportunities for women in impoverished and conflict-ridden areas of the globe. And this is kind of a cool feature - when you receive your dress (or shirt, etc.), you can check the tag to find out who made your garment, then visit One Mango Tree's artisan's page to see a photo of the woman who created your item.