I can't implement an asteroid mining program now because the cost of space launch for the preliminary/prototype mining equipment would be prohibitively high.
If I had access to a space launch capability for less than $100/kg, however, I could bootstrap the whole business from my basement with an investment of ~$100-200k from some friends. [0]
From SpaceX's perspective, they can put ~5 tons in lunar orbit for a cost of $200k in fuel [1]. $40/kg is great, but it's not what they charge their customers, and it's not what they'd charge me - demand from comsat operators with a much higher willingness to pay means that I have no access to the market, and SpaceX needs to make a profit.
Give it 10-50 years, and I'd expect real asteroid mining will become economically viable. [2]
[0] assuming zero NRE for mining robot fabrication and a single person salary.
[1] ignoring actual launch costs, personnel salaries, and assuming the whole booster stack is paid for through infinite perfect recovery.
[2] see also Planetary Resources, and why they should be in hibernation mode, not burning $2m/year developing camera sats. but hey, VCs have money to burn.