Is it impolite to ask how much money a person paid for their house?
Yes it is. If you are considering buying in the area you could
say, "My husband and I (or my wife and I) are considering buying a
house in the same area. Do you mind me asking APPROXIMATELY what
houses are going for around here?" Either this or phone up one of
the Real Estate Agents (there should be signs on the lawns of the
homes that have been sold or are still for sale.)