We make this a must do every trip. In fact, my 7 year old daughter has only gotten her hair cut at Magic Kingdom. But they do a gel and pixie dust treatment for girls (you don't have to get a haircut). Basically, they take your hair and put it in a half pony tail on top of your head. They then put stripes of gel up from your hair line on your forehead to that pony tail and top it off with pixie dust. It is a ton of fun. As to cost, I think we paid between $7-9.
And as an FYI - you can call and make reservations with the Barbershop by calling Disney Dining. If you get a CM who says that you can't do that, hang up and call back til you get a CM that knows how to do it. And note that you can only reserve two spots per 30 minute time slot. They will also take walk-ins but those with reservations get taken first.
It is a great alternative to BBB so have fun!