I don't see how asteroid mining can be viable economically. You still need an enormous quantity of petrol to send things in space and judging by the rarefaction of said petrol its price is bound to increase a lot.
Instead of one giant rocket, imagine swarms of small, reusable, low-emission projectiles whose payloads assemble into larger apparatuses in space.
You need to think out of that box - I'm investing my savings in hevea plantations !