Mining Asteroids Too Hard?

In a post that I'm studying a bit, I have come to a few preliminary conclusions that it is too hard now, but perhaps not later.  Launch costs have to be reduced eventually, or we all stay grounded indefinitely until it does.

He uses a mission cost of 600 million dollars in his example.  But he doesn't break it down into its various components.  How much for the mining equipment and launch costs separately?  What can realistically be reduced?  What can be improved upon?  The yields for the mission seem low.  You don't want to go all the way out to an asteroid and only mine 43 million dollars worth of the stuff.  You have to have higher yields or it doesn't make sense.  That would be true even if you got launch costs way down.

It may be hard to mine asteroids profitably at these assumptions.  Maybe the assumptions are all realistic.  If so, even in the best cases, and with launch costs much reduced, we still may not see much mining of asteroids.

The yield is too low.  Can you do any mission like this for 43 million?  Even with lower launch costs?  I was thinking of a yield of half a billion and launch costs much lower.  That would leave plenty of room for profit.