Ok, people pointed out the complete bullshit number about the actual - inflation corrected worth.
But there is another vector that needs to be taken into consideration, that has a devastating effect on bigger space mining undertakings.
To make it short if done on a big scale space mining could change the earths orbit and rotation period.
And this is what most fly-highs do not take into consideration.
1.) every planetary body in our solar system is there and "does" that because it has a mass, and a certain kinetic energy
a.) also mass distribution plays a role (moon tide = earth has changing mass distribution, "wobble, wobble")
3.) these properties make the planetary bodies move in such elliptecal shapes as they do.
From 3.) change them by mass and the momentum/energy that is "glued" to the mass, you change how the planetary bodies will behave.
Yes, this happens contiously. Earth is loosing as well as gaining mass - naturally. Helium can escape the atmosphere, but meteors are hitting the earth, transfering mass and energy.
And the Apollo missions transfered mass to the moon.
The key point is the scale you'd do that and when thinking in "deathstar" categories you can predict a big change.
If you can't imaging it, go ice skating and do a pierotte and pull your arms to your body.
What in consequence might happen I can only guess , however I know something will happen.
Because you change the system on a big scale.
I call this the real "masseffect"