Wendell Cox ponders the question in this newgeography post. The short answer: very far, indeed, especially in markets where building is stringently regulated.
Cox’s money grafs:
But my guess is [Issac] Newton is still a very relevant person. If so, we should expect additional price decreases of 30 percent or more could occur in already declining markets such as Los Angeles, San Diego, Washington, D.C. and Miami. Similar declines from now could take occur in places like New York, Boston and Seattle, which have only recently experienced a downturn in prices.
Of course, it is always possible that smart growth regulation in these markets might have created a new floor that prevents prices from falling to historic norms. That would be good news for the owners of real estate – largely older and Anglo – in these areas. On the other hand, it would be disastrous news for millions of households and the next generation, many of them younger and minority, who will now have to remain on the sidelines of the housing markets of their choice. For many the choice may be moving to one of those places – like Indianapolis, Dallas-Fort Worth or Kansas City, Houston or Atlanta – where the opportunity to own a home still will exist for those without trust funds and elite occupations.