I agree with what Informalbride said.
If you are happy to give them a colour scheme but let them choose their own dresses, it's ok to ask them to pay, but if you want something specific, you pay.
I've asked mine to provide their own shoes - I'm not worried about them matching and would rather they wear a pair that they already own and are comfortable in, as well as saving a bit of money.
I'm probably not going to book hair and make up, as most of them are pretty good at doing their own, plus I have one friend who is allergic to everything make-up and hair product-wise, 1 girl has short hair and 1 has braids, so it would seem a waste of money to spend a lod of money for someone to put a flower clip in or something! And I don't want o seem like I'm favouring anyone by paying for some but not others!
I have 6 BM's (and 2 flowergirls) but managed to get beautiful tulle skirts on Amazon at a great price. I'm pairing these with a simple vest top, but the whole outfit should come to about £50 each (including flower crowns). Buying stuff in phases makes it feel like less money!