I haven't ever been to BBB b/c I have all boys but if you want to do something fun with their hair and not pay for BBB remember that the barber shop on Main St. will put thier hair up, has colored hair gels, and will sprinke pixie dust (i.e. glitter) in thier hair. :)
Here are some pics:
Yes, you have to buy a package and yes it is totally worth it. My suggestion is to get an early morning appointment so they can have their hair up all day.
If you want to spend that much money, it's definitely worth it.
As others have mentioned, yes, you must pick a package from those offered at BBB. Here's info on them:
Val, Co-CL Disney Vacations