Ultra-low interest rates mixed with stabilizing home prices continued to push housing affordability in the 3rd quarter near its highest levels in more than 2 decades, according to the latest National Association of Home Builders/Wells Fargo Housing Opportunity Index.  For the 3rd quarter, 72.9% of all homes sold were affordable to families earning the national median income of $64,200.  Prior to the past 11 quarters the Index rarely was above 60%.  With interest rates at historically low levels & markets across the country are now within the reach of more households than it has been for nearly decades,  according to Bob Neilson, chairman of the National Assoc. of Home Builders.