With drones, it's not just a cost saving on pilot or machine, it's also no airways fees or landing fees. No transit times (flying to or from job site). Initial outlay for equipment probably only a single digit percentage cost of a full size aircraft. Pilot training/legal stuff probably a similar percentage and maintenance costs near zero. Bit of electricity for your batteries and off you go.
Saw a promo about drones in Dubai a while back. Apparently drones were being looked at for solar panel and high rise building exterior inspections because it was cheaper then having crews manually climb and physically inspect the panels and buildings.
Real estate agents love em. Lots aerial photos in the local paper.