Let's open the discussion about a topic that is rarely brought up... bridesmaids beauty etiquette. When you ask a friend to be in your wedding remember, they want to be there for you even though it can be incredibly costly. Yes, in the grand scheme of what you are spending, their financial responsibility is small but in reality they are buying a dress they probably don't love, shoes, jewelry, sometimes a plane ticket, hotel, a present, make that presents for shower, bachelorette party and the wedding, using vacation days even though they will not be relaxing with their toes in the sand but doing their best to be there for your every whim and need as your special day approaches.
In my experienced opinion (1002 weddings and counting) since the photos are incredibly important to you in cost and memorabilia so YOU as the bride should strongly consider making sure your bridal party looks their best with professional hair and makeup. When it comes down to it, they can't say no to the dress or the plane ticket or the parties or the presents but they can draw the line at paying for their hair and makeup which only hinders YOUR photos.
My strong suggestion is when you get engaged and are planning your wedding budget, factor in hair and makeup for your girls. I would recommend about $150 per person plus 20% gratuity if you are thrilled with your services.