How long do you think it would take for the US government to build 100 million killer robots?

I don't believe that it ever will.

Technologies become less expensive over time, and as we progress, our wealth grows. If we don't have the money to produce it at the current cost, that doesn't mean they'll never be able to afford to do it.

If the US spends 6,000 USD in maintenance per robot, that would eat up the entire US military budget. 6,000$ is almost certainly a severe underestimate of the cost of operating them, by roughly 3 orders of magnitude

You didn't specify a time period - should I assume that's yearly? Also, do they have to pay $6,000 in maintenance costs while the units are in storage?

and anyways, that neglects a huge number of relevant factors: the cost of purchasing an MQ-1, amortized over a 30-year operating period, is roughly the same per year as the operating cost; money also needs to be spent doing R&D; non-robot fixed costs total at least 6% of the US military budget; much of US military spending is on things like carriers or aerial refueling or transports whose robot equivalents wouldn't be 'killer robots'; etc. (The military budget may go up over time, but the cost per plane has risen faster than the military budget since WWII, so if anything this also argues against large numbers of robots.)

Okay, so an MQ-1 is really, really expensive. Thank you.

An alternative date: I would expect the USAF to be majority unmanned by 2040 +- 5 years (50% bounds, most uncertainty above); this is roughly one lifecycle of planes forward from today. (Technically it's a fair bit less; but I'd expect development to speed up somewhat.) I would expect the US Army to deploy unmanned ground combat units in serious numbers by 2035 +- 5 years.

What is "serious numbers"?

I would expect the USAF to remove humans from the decision making loop on an individual plane's flights in 2045 +- 5 years; on a squadron, including maintenance, command, etc, 2065 +- 5 years; above that, never.

What do you mean by "above that, never"?

Sorry I didn't get to your other points today. I don't have enough time.

P.S. How did you get these estimates for when unmanned weapons will come out?