Hair for bridesmaid

If you require a certain hairstyle, then you are obligated to pay. However, if I were you, I'd have a conversation with your girls and ask what they think. Let them know what you would like, and if they tell you they aren't comfortable with that then you can go from there and decide if your vision fits your budget.

If you are requiring it, you have to pay for it 100%

Agreed w/PPs - anything specific aside from the dress that you're requiring you're obligated to pay for. If you are allowing them to choose whether or not to have their hair professionally done, then you can either offer half or let them pay, so long as they understand it is their choice.

If it's required, you should pay for it. If it's optional and the girls can pick if they want it done or not, they can pay for it. Especially since they were required to get specific shoes.

I was in my cousins wedding and she offered for us to have our hair done by the stylists that were doing her hair, and it would cost us each $50. But she also gave us a gift at the rehearsal dinner that included $20 for our hair, so it wasn't as much out of our own pocket.