Underground housing, underground businesses, etc. Would that be better for the environment + possibly save on energy costs? Also possibly safer in certain scenarios like tornadoes etc.
Potential issues that immediately come to mind are ventilation, earthquakes, and flooding. But it’s not like underground dwellings/basements/etc. aren’t a thing, so maybe those issues have been addressed in ways I’m not familiar with.
Do you want to suggest a measurement scheme in which underground building is cheaper? As is I don’t understand your point.
Do you consider lifetime costs? Do you consider the value of biological services of an undisdturbed land surface and habitat? Do you consider the value of a lifetime of energy savings for heating and cooling? Do we factor climate change opportunity costs? Do you consider the disaster resilience of a subterranian building built once vs the multiple constructions of a tornado or hurricane built and rebuilt?
Sometime what seems cheapest can be the most expensive.
For a single family dwelling (or any structure that isn’t too deep), reduced heating a cooling costs could make building underground cheaper in the long run.
For a large structure that goes deep, I doubt if it could ever be cheaper to building underground.