IMO, there is some market for private self driving cars at almost any price, if it's usable and legal. The minimum volume at which they can be produced, legalized may be too high though for any kind of niche luxury market though.

The path to substantially replacing human driven cars though is (I think) some sort of driverless taxis. The price where driverless taxis take over is probably somewhere around where the cost per km of driverless is lower. That could be pretty high. Assuming other operational costs are similar to regular taxis $150k-$200k for a driverless vehicle that lasts 3-5 years sounds viable.

Driverless cars have been sitting around the edge of our consciousness as "experimental but interesting" for a long time. But, the economic changes they introduce are potentially enormous, wide. I think there's a good chance that privately owned cars become rare, for example. General purpose cars may go away. A golf cart is just fine for going 5-10 miles in urban traffic.

This space is big enough for Google/Ford/IBM sized giants to emerge in. Makers of the cars, makers of the driver, makers of the UI, operators of the taxi companies, who knows what else. Maybe makers of digital roadsigns. Maybe selecting destinations from a screen creates the kind of effect Adwords has had.