The dresses are really expensive.
As a general rule, the bride should not require bridesmaids to pay for their dresses if her pick is astronomically pricey, say $300 or higher. Either cover the cost, pitch in to help pay for the expensive dress, or decide on something that's affordable for everybody!
The verdict: Bride pays, or at least helps pay, when the chosen dress costs a lot.
Source: Bartlett Pair Photography