Food production is already plenty cheap in the developed world. In the 50s in the US middle class people still worried about the price of milk and butter and the working class did not have the option of eating out for every meal. Even Mexico, a middle income country, has an obesity problem rather than a malnutrition one.

In areas with high demand the constraint on building housing is zoning, not cost of construction. You can build in masonry up to eight stories high as long as you have elevators. With steel frame much higher obviously. Everywhere the cost of housing is substantially above construction plus land costs the reason is zoning.