if you plan on getting your pup fixed there really is no difference.... if keeping them intact a male will be harder to train as he will try and mark all the time...females will have a period during every heat, which i would prefer not to deal with, lol! its better to get them fixed anyways!!
there is a myth is that boys take to girls of the house and girls take to guys of the house.... but it is just that, a myth
i would say visit the pups and pick which one stands out to you
as for charging more for a female most good breeders shouldn't.... if you're getting a breeding chihuahua a female can be more sometimes though...
akc should have a listing of breeders and there may be one close to you,
hope that helps