I have been asked that a few times but by friends or family not complete strangers. I simply say "You can put a price on love" but then I tell them IF serious about adding a Yorkie to their family, that it all depends on age, size, breeder etc.
My mother who is a police officer has been wanting a Yorkie as well...and I am looking into helping her adopt a spayed older female being as though she isnt home enough for a young puppy. The people who have adopted Miley's mom is paying $450.00 for her but she is being spayed before going and all vetting is taken care of before she leaves.
So depends on what a person is looking for...thats what I say. If youre wanting a teeny tiny champion bred Yorkie youre obviously going to pay more than a spayed 7 yr old adult pet quality Yorkie.
I try to inform the person as much as I can if they are interested in adding a Yorkie to their family but if they are just being nosey I say "Not nearly as much as she is worth" or "You dont buy your children...you are blessed with them"