It's possible they'll be even cheaper but that range is the cost according to the IRS of operating a typical vehicle all in, and that seems like a reasonable guess of the cost of an autonomous electric vehicle with far lower probability of crash than a human (all the savings basically going to profit margin).
At ~60¢/mi, there'd be a lot of people who would save money on balance using autonomous taxis to get everywhere vs owning a private vehicle (10k mi/yr would cost only ~$6k/yr, a pretty low cost of ownership/use for a private vehicle).
