The cars will be mechanically simpler (electric motor connected to wheels without a traditional gearbox), require less maintenance (no oil changes), be cheaper to insure, and inexpensive to operate. The electronics and software will do what they always do - get better and less expensive. Lighter cars that don't crash (often) can be made from different (cheaper) materials than current cars. They will be similar to today's golf carts. I think a basic car will cost less than $10,000.

A lot of the same innovations that go into producing a self-driving car apply to the construction and repair of the car itself. One of the most expensive parts of a new car is paying for wages, benefits, and pensions for the people that made the car. I'm thinking self-driving cars will be built and serviced by other machines. I would bet that before long, you buy a car the same way you buy a cell phone. You subscribe to a plan and upgrade every 2-3 years. Maybe you would subscribe to a shared fleet for $50 / month or maybe you "buy" your own car for $250 / month.

This is all assuming a few years have passed and human driven cars are rare.