What are the most affordable, interesting cities in the U.S.?

My wife and I love New York and San Francisco, but they’re not cheap—particularly now that my wife and I have a son. Chicago’s a great town, and the real estate is more affordable, but Illinois’ budget problems is making us hesitant to move there. Austin, Asheville and Portland (actually both Portlands) are all nice, but we don’t love them the way we love NYC and SF. Anyone have other suggestions? Low taxes and good weather are plusses, but mainly we’re looking for an interesting city with an interesting mix of cultures and restaurants, yet affordable real estate and a solid economy. Does such a place exist