IIRC, in SF they're slightly more expensive before tip, but having ridden in them in SF, LA, and AZ I've always felt they were cheaper. Over the long run, they will probably end up being cheaper from the wholesale perspective since eventually the parts and technology cost will come down with time and scale while human wages will continue to rise.

That said, it doesn't really matter if they're cheaper as long as they're comparable.

The cars are newer and nicer (for now), they're almost always cleaner since they can rotating one car out for cleaning doesn't mean the driver is losing earnings, they're better drivers than the average ride-share driver, you don't feel the need to tip, and I've multiple of my friends who are women call out that they feel safer in them because there's no risk of the driver being creepy (or worse).

I don't think Waymo is trying to win on price right now. I think as long as they just stay somewhat competitive on that front the other benefits will continue to draw in customers.