Obviously this idea sounds ridiculous to many economists as there is no particular reason to think it makes sense to go through such lengths to get natural resources. After all we live on a pretty darn big spacerock.
To the extent natural resources are expensive on earth it is because they are difficult to get at, not because we are running out. There is of course some possibility that they would be actually easier to get at in space. The problem is that doing so is a major project that only makes sense if you can bring back a lot of resouces.
However, the very reason that hard to get at resources on earth are expensive is because the limited quantities cause consumers to bid up the price. If there were many more, then the bidding would be less furious. So, you face the problem that as soon as you bring a huge chunk of gold or what have you back to earth you cause the price the crash and cannot recoup the mission costs.
That said, there are two things.
One, is that in theory the company could sell some type of speculative contracts on the minerals it hopes to get. Basically you need a contract that says, of the first X amount of mineral that we bring back you will buy it at Y price. Then these contracts would have to be sold in series with the understanding that the total draw down from the mining operation will be uncertain both in terms of beginning time, quantity and duration.
So they can try this, though I am guessing the price for such contract will not be that high.
Second, this actual strikes me as more like Craig Venter’s stent at Celera Genomics where a private company was used to do basic scientific research and the investors bought in, in part because they wanted to be a part of something great and in part because the scientists more or less conned them.
Though as wealth dispersion increases and people get richer I think this “Invest for Prestige/Get Conned” model will be big for science.