A bottomless well of money and an ability to hypnotize Wall Street with promises of an autonomous driving future. He’s starting to run into the limits of both.

Tesla shares have surged in anticipation of the launch of the company's robotaxi service in Austin, Texas, this week. Goldman Sachs says Tesla has advantages in the AV market, but questioned its ability to meet CEO Elon Musk's targets.

The question is whether the cost can come down to make robotaxis profitable—and competitive with Ubers, public transit, and even private cars. To fundamentally reshape urban transportation, robotaxis have to be both functional and cheap.