Growing up over here, we're lucky because every girl pretty much has to have a white muumuu. Muumuu are not all big and frumpy and they won't make you look like a balloon. You can get them pretty much anywhere here for cheap. Usually each new member class in my chapter makes an outing to the swap meet/flea market and depending on how many they buy they can get one for less than $20. They look great...and uniform!
This one might cost a bit more, but this is the one I want to get especially for Convention:
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