Google are going to scope out basic partnership agreement frameworks with the companies interested in making partnership agreements with them, and if that happens to be a premium vehicle manufacturer then so be it. If they wanted to invent a new kind of "long life, extremely cost-focused vehicle" it would take them much longer anyway, and be entirely unnecessary to successfully challenge an app company making a loss in most markets and running out of runway. What really matters is if, when and where Waymo have self driving tech adequate and legal for commercial operations.

In the unlikely event of Waymo actually ordering 20k Jags, the economies of scale they'd get would be enormous even compared with non premium Uber vehicles bought on finance at dealer prices even before the driver gets paid, and many taxi markets use premium vehicles by default.