I did some googling and math. Global platinum market is 8 million oz a year. Current spot price is ~$900. That’s $7T per year. They would have a monopoly and be able to shut down all mines by undercutting the price selling at say $800/oz. If it cost $40 Billion to mine the asteroid, that means it would take 7 years to pay back the cost.

7 year payback is short for businesses. Commercial Solar is installed despite having a 10 year payback.