Deep sea mining seems more likely. The most valuable component of ferromanganese crusts, or manganese nodules, was the cobalt, even in the 1970s. More so today.

I don't think that the concept of asteroid mining is totally ridiculous, but I think it needs to be uncrewed, slow, with low delta-v. So even if you had a target asteroid and a robotic mining system all ready to go today, the products wouldn't reach terrestrial markets before a couple more decades passed.

What about the philosopher's stone? Surely with enough research in alchemy and Elon Musk's support, we could tweak it so that we can conjure all metals from thin air.

Dude.