They won't be cheap until there's competition to drive down the price, which will otherwise be as high as possible to justify the initial investments. It's only a matter of time, but likely on the scale of decades.
replyBut I wanted to add on the future benefits front - as more vehicles on the road become autonomous, they could communicate with each other and reduce the buffer distances between them, allowing for faster travel and improved saturation while still being safe.
It won't be cheaper.
reply1. If auto cars will be cheap, every one will use them, and none will use public transportation.
2. Oh yeah, we would just waste space outside the city.
3. Right now it's not safer. It will probably drive at the speed of 25% less than the limit, sure than it might be safer.
1. People already don't use public transport in 99% of the world. In any case I don't see why that is relevant to the price.
reply2. Which is vastly better than wasting it in cities. And also no we wouldn't. Autonomous cars would be in use way more of the time than normal cars so we'll need fewer of them and therefore less parking space.
3. RTFA.