The IBM 650 computer from the 1950's would cost you $4 million in today's dollars, and yet here you are sending us messages on a PC today @ 1/8000th's of the cost and suffice to say what you have is millions or billions of times faster and has a similar increase in memory (I cant be arsed to do the math)
As for hardening the equipment against attack, it will increase the cost, but isn't a technical challenge.
True, but that took 50 years. And cars on the other hand didn't become much cheaper. It will not be terribly difficult to disable one with an rpg or something I imagine. Even when you strap on all armor it can possibly carry. So what do you have in the end? Something that's somewhat tougher and with more firepower than an ordinary soldier but which can't go up stairs or might even have problems sorting out its legs when you throw a blanket over it. All in all it's not terribly scary, not compared to the all the other things that long exist.
As for decreasing costs I'd think what will become really cheap in the future is human life. Why are modern computers so cheap (*)? If you think the robots will become quite cheap, do you think they will be made in China? I am not at all against technology or globalization. But I do not think the technological revolution we had was economically sound (the costs were hidden though). We are only beginning to realize that now. And the other question is, instead of building killer robots why not go for fully autonomous agriculture, textiles and stuff and send all the new unemployed to the frontlines with a cheap rifle?
(*) One part of it certainly accounts for the initial investments being covered. Which is why noone cares about space mining. Even if establishing the necessary infrastructure only costs 50 billion $ and there's no extra running costs, you are not competing with companies digging it out of the earth and paying exactly 0 $ for such things. The other part invariably comes down to people producing more for a lower wage if you recurse long enough.
