Re: Who are their lawyers?
"I wonder if 3 shifts/24 hours of manual labour for a year costs more or less than the $20,000 Musk reckons his humanoid robots will cost?"
More. I found a few estimated average for Amazon's warehouse workers in the US ranging from $15.50 to $17.00. There appear to be some jobs and locations significantly exceeding these, but they didn't provide enough information to filter out higher-level supervisor jobs in the warehouses so I can't confidently use those. I know they've talked about increasing that and may have done so, but let's assume these are still accurate. In fact, let's assume these are overestimating and use a nice round $15.00 per hour.
If they have absolutely no overtime, then wages alone for a single worker-year (full-time 8 hour shifts 5 days a week) would be $31,320. Extending that to a single worker for every hour in a 24/7 setup would be $131,400. Amazon also has health insurance benefits, payroll taxes, unemployment insurance, and other expenses, so these numbers are significantly below what they have to spend.
The only problem is that a humanoid robot may not be able to do what a human can. I don't work in robotics, but I know enough people who have to watch them do a lot of work to get a robot to do something that comes very naturally to a human. If the robots are to be deployed in an environment with unplanned obstacles and for tasks without an easy deterministic answer, the robots may be incapable of reaching the efficiency of a human.