The only restriction is a common color scheme.
If you want to stick to a specific color palette for your nuptials but don't care about the bridesmaids' individual dress styles, your maids should be able to choose a dress that they'll wear again. Because of this, they can invest in the pieces themselves.
The verdict: Bridesmaids pay, because they chose the dresses and can wear them again.
Source: Michèle M. Waite