For anyone curious, if each ride takes 10 minutes, and the car can spend 8 hours a day doing rides, it would take 5.7 years for a car to give 100,000 rides. (I added a little to accommodate the price of charging the vehicles and maybe some maintenance)

I think this is pretty reasonable considering that for $5/ride I would expect there to be quite a lot of demand, and there's opportunities for things like food delivery as well.