My bikes cost a lot compared to most on the road. I think it's not very polite either to ask how much someone's bike cost them (unless it's a close friend who's interested in bikes).
When strangers ask me how much my bike cost, I just say "more than the bikes at Wal-Mart." If they continue to press, then I just say something like: "Well there are all kinds of prices levels bikes, depending on what you are looking for in a bike...Why, are you thinking of buying a bike?" that turns things around pretty quickly.