Um, why not do it yourself?
That's what our extended family has always done. All you need is a costume, hair glitter (always go outside your room to spray!), and maybe a tiara. A tiara is easy enough to obtain.
If you want to do the nails, why not just do it locally before you go? That way, it won't just be the princess who gets her nails, but mom can get nails done too, and you are using precious vacation time to do it - esp super limited party-ticket time.
I'm not being mean, its just that when I'm at WDW, I try to focus on spending my times doiing things that an only be done at WDW. I consider getting beauty stuff to be something that can be done off WDW property.
that said, the barber shop is a fun little spot for a Disney updo/hair trim.