Using a random driverless car will be much cheaper than owning (perhaps roughly as expensive as taxis would be if there were no taxi driver who needed to get paid). Random cars can be in use virtually all-the-time every day. The portion of costs a single passenger pays will thus be small fraction of the total costs. For a car you own, at least as it works now, you generally pay 100% of costs. So it's not going to cost just "a little extra" to own your own car; as it works now owning a car results in huge levels of waste, while the expensive item sits doing nothing, occupying a (valuable) parking space.

I suppose you could own a driverless car and have it continuously deployed as an income-producer moving other people when you're not using it. That creates a lot of additional headaches and problems, though. E.g., how to make sure it's always available whenever you decide you want it? Or, will it be safe to leave your items in the car when it's used by others? (I would guess not).

As a city dweller, I would take random car over random parking spot every single time. Certainly does not apply to those who already pay a little extra for private parking though.