Every car is more affordable when you don't have to pay a human being to operate it. The difference in labor costs dwarfs the difference in vehicle costs.
It's been a while since I looked it up but I understand the human is about 50% of taxi operating costs. That's not trivial of course but it's also not dwarfing vehicle costs.
Why? They have started unsupervised taxi rides in Austin. One of their goals was affordability, and their cars are massively more affordable.