"Prospecting probes can likely be built for tens of millions of dollars each and Caltech has suggested an asteroid-grabbing spacecraft could cost $2.6 billion."Asteroid about 100m across could be worth about $50 billion, so the profit is there.
Usual warnings about crashing the world economy etc. But making raw materials cheaper won't crash the economy; it'll only crash the holdings of people who have a stake in keeping them expensive. "I'm Joe Ironmineowner, and I oppose asteroid mining!" "I agree! I am Cheng Palladiummineowner and I want asteroid mining stopped now!" "I'm Bob Aluminumcancollector and I hate asteroid mining!"
It's the entrenched interests that are the problem. But like Democrats in antebellum America, one may as well shout at the wind; you can fight against the coming changes all you like but economics rules with an iron fist.
Thing is: with SpaceX poised to reduce the cost of getting a pound into orbit to stupid-low territory--well, one of those Falcon 9 boosters that makes 10 flights before requiring any overhauling would reduce the cost of the booster by 70%, enabling a significant cost reduction over "use it once and toss it". It's going to happen. It's economy of scale.
Economies of scale also work for robot prospecting probes. "Tens of millions of dollars each" if you're building one-off probes; the instant you set up an assembly line, that price drops.
And think about this: corporations originally were formed to finance expeditions to the new world. Once we had the ability to reliably cross the oceans, people would pool their money to hire a ship and crew and outfit it, and send 'em off...and then reap the rewards when the ship came back, or wonder idly whatever happened to that ship...? (Hence "Someday, when my ship comes in....")
There is absolutely no reason people could not do the same thing today with a robotic prospecting probe. They buy the probe and the launch, and when the probe strikes paydirt, they place a claim and sell the asteroid to the highest bidder.
But then, one corporation's probe finds something unusual and spectacular, and then the race is on to--whoops, I'm sorry, I slipped into SF writer mode for moment there.