It looks like they'd have to redo a significant portion of the front of the building to make it work, from the street up to the patio, then up again to the door

It looks like they'd have to redo a significant portion of the front of the building to make it work, from the street up to the patio, then up again to the door. (Which, itself, may need replacing.) My guess is that $100,000 is a rounded up, order of magnitude estimate rather than a specific amount.