As far as fueling/charging- Even if you had to pay a few people in the short-term to do the work, it isn't a high-skill job. Being generous, I can't fathom a situation where it could cost more than $2 per car in physical labor. Assuming you could drive more than 200 miles on a charge, that is less than a penny per mile in cost. Also, there are already gas stations in some states with people that will fill your gas tank for you. I am also sure an autonomous solution would be devised if that became a limiting factor. You could pretty easily design a purpose-built system for it.
I agree that regular maintenance needs to be performed, but I don't agree that the companies themselves need to solve the problem on their own. This seems like it would be something to easily contract out to a local company to handle. For standard maintenance and cleaning, there are plenty of companies that clean cars and plenty of companies that perform maintenance on cars already. It should just be a matter of getting contracts in place and making sure that they have software to do their jobs.
I didn't do the math to figure out the cost of a human driver vs the total taxi cost, but even if true the cost isn't trivial. Truckers, for example, can make upwards of $80k per year and that's not even at 50% utilization for the vehicle. If you assume a taxi driver would make $40k/year and they have 50% utilization of the car (I'm making up numbers for the sake of discussion), that is still a significant amount of cost. I would be surprised if maintenance and fuel would be $40k per year regardless of vehicle.