I bought my BMs dresses. I decided that I would since it will be pretty spendy to be at our wedding. Plus they are my sisters, and I wanted to help them out...especially since 2 of the 3 of them are very young (18) and don't have much money anyways!
I just kept my eye on ideeli.com for dresses that I liked, and ended up getting 3 pink convertable dresses for $69 (reg $198) each! I will also buy them necklaces and hair flowers and leave their shoes up to them.