Ragunathan Rajkumar, a professor at Carnegie Mellon who is developing self-driving car technology, says that for $700 or $800 the parts can be bought to build such a system. After markups, he estimates that consumers will pay an extra $2,000 or $3,000 for the initial cost of their vehicles. That up-front cost probably would pay off down the line through lower insurance premiums and greater safety.