Automines and mass drivers are your cheapest bet, they can both be delivered by civilians, which saves you fuel and micromanagement headaches. They can also be shipped to planets when their asteroids are mined hollow.
I recommend working on jump tech though, and searching nearby systems. You'll probably find some much larger sources of everything. For instance, it's not uncommon to find planets with tens of millions of multiple minerals. In my current game, I have a planet with over ten million of everything but Tritanium. Which is no problem because other planets in the system have millions of that.