I can understand in a situation like gemy and some other posters . If the person is asking for educational purposes or perhaps they are thinking about buying a particular breed, then of course a generalization of the cost is fine. But most times folks are being downright nosey and rude. I would never ask how much "you" paid but I would ask for an general estimate. A general estimate would give an interested person enough information.
I would be very cautious of strangers however because crime and theft may be the reason for the questions.