Lost Garage Epidemic

3 of my favorite neighborhoods, Shaw, Tower Grove East and Tower Grove South have many, many properties without garages. The foundations appear to be there, even remnants of walls and other various structures exist. But, I've got to wonder: what happened to all the garages in Shaw and TGE?

What do you think it would run to build a new garage? Has anyone out there done this, either themselves or contracted it out?