Can someone help me put this into context?

$30/month is way cheaper than $104/month.

How would you compare the base metrics?

Time to start traveling, average walk amount per trip, total trip duration, coverage parity, etc.

I suspect you can get into a waymo quicker and with less walking than a subway, unless you live very close. I imagine total trip time is pretty variable. Coverage parity is hard to guess about - in theory a waymo can go anywhere but I suspect public transport has longer "tendrils."