I was hoping that someone that knew for sure would answer this yesterday because I can't give you a complete or definite answer. I don't know how much the dolls cost at all.
We have bought the clothes and as I recally they must cost around $25-30 or so because my girls have to buy their souveiners with their own money and that is about the amount they ususally have.
The dolls and dresses are hard to find. I know we found them at Once Upon a Toy and The World of Disney Princess Room, and you may find different princess outfits at each location. I think the toy store didn't have the one that my dd was looking for but the other location did so you may need to shop around.
I hope someone else can help you with the price of the doll. My girls just bought the clothes for their American Girl Dolls so we never looked at their doll.