The '03 Crown Vic has long since paid off it's capital costs and the cab company gets to blame the driver if things go far enough south for lawyers to get involved.
Until some mythical future where self driving cars are so good and common that the "progressive" states start providing financial disincentives for people to operate their own vehicles (which would be a pretty major about face the vast majority of all transportation and infrastructure related regulation to date) I don't see where the driver-less taxi has a cost advantage in the foreseeable future. Your insurance premium is in large part based on the presence of everyone else around you.
It doesn't matter if the cars cost 100K, the driver wages still are larger than the capital costs.
You can already look at Uber pool, which is a direct tradeoff between cost and speed.