That’s government doing it. Planetary Resources and DSI are private companies.
You are also thinking in terms of 60’s technology. My iPhone has more computing power than all of the computers used in Apollo combined...
And then there is this...
https://en.m.wikipedia.org/wiki/RF_resonant_cavity_thruster
Game changer...
Bring it home? the dinosaurs tried that and look how it worked out for them.