From an analysis I saw, AB-5 is expected to cost them around $500m per year. Even though prop-22 would still be more expensive than their pre-AB5 costs, that's a pretty good ROI if they succeed.
Thanks for mentioning this, a tweet that said Uber spending so much on campaigning/lobbying shows that they can pay drivers went viral and drove me a little nuts with the clear lack of thinking involved.
Notice that in my comment I said "invest in figuring out" and not "pay drivers with." personally I doubt that it would cost a half billion dollars - that's farcical even at California scale. But the point Id raise is it costs less than 180 million to reorganize and set up insurance coverage for your drivers, payroll, and other internal infrastructure to comply with the law.
But complying with the law is antithetical to Uber's culture, so it's not surprising that the thought of obeying the law never crossed their minds.