I imagine autonomous taxis will be significantly cheaper than driver taxis. From a quick search it looks like in general Uber drivers earn somewhere around $9 for a 30 minute ride [1].
And out of that $9, the driver has to pay for their gas (or electricity) and upkeep of the car. Uber apparently earns about $3-4 for their service. If Uber is now covering the costs of an expensive for now autonomous vehicle, it's not clear to me the fare drops at all.
[1] https://blog.completepayroll.com/fares-driver-pay-and-the-fi....