You can find out where they are by reading the following article:
The 10 Most Affordable Housing Markets
But if more people move to these cities, prices in those cities will rise and they won't be very affordable anymore. This illustrates what economist Steven Landsburg calls the "Indifference Principle."
"Except when people have unusual tastes or unusual talents, all activities must be equally desirable."
So unless you really like where you live or you have no interest in moving to these "affordable places," they will not stay very affordable for long. All the people who don't care about where they live and only want to minimize cost will start moving there. But that will drive up costs. If people don't move there because they don't want to move to those cities (like Youngstown, OH or Indianapolis, IN), finding out that they are "affordable" won't have any effect on them.