Bridesmaids shouldn’t pay for their dresses
If you ask someone to be in your wedding as a bridesmaid or MOH, it is tacky to make them pay for their own bridesmaid dress. While it is true that they could just decline to be in your wedding, you as the bride are asking because you really want these particular people in your party. Your bridesmaids are doing you a favor, even if they are happily participating, and asking someone to be a part of your big day so it can be what you want it to be and then having the audacity to expect them to pay for the necessary attire YOU want is ridiculous and rude.