Google isn't the only company developing autonomous cars. Multiple car companies have own working prototypes. So it doesn't look like there's any monopolization of the technology itself. It seems likely that the capital cost of an autonomous car will be roughly comparable to the capital cost of a normal car.
Sure, but a self-driving car by itself is of fairly limited utility in a taxi operation; the advantage that they provide comes with the data gathering and analysis system that provides centralized control of the fleet. Automation, as it matures, should drive down the per-car cost and drive up the competitive advantage of the player that can expend the most on central resources.
When you reduce the relative importance of the per-unit cost and drive up the relative importance of centralized costs, you make a market that has stronger natural tendency to form a monopoly, because there is more of a positive feedback loop reinforcing the position of the leading player.
