i guess it depends on the breeder you get your baby from...even some very good reputable breeders will charge a little more for the smaller ones because maybe they were hand feeding for the first 4 weeks or so? or maybe (other than the size) are closer representations of the breed (topline, earset, etc) but most breeders (good and bad) do charge more for girls than boys
i know of a great breeder who actually was charging more for a bigger girl because she was closer to the standard than one of her smaller ones