Thunder Horse

This idea of Mining The Sky for its mineral wealth has its counterpart here on the ground, or at sea.  Just to show that big projects funded by private funding is definitely possible, witness the Thunder Horse PDQ drilling platform in the Gulf of Mexico.  Construction costs came in at 5 billion dollars.

I think it is worth noting that "tethers" are used in construction all the time.  Most folks just don't see them that way, but the principle is the same.  For example, the cables in a suspension bridge perform the same function as they would in outer space.  They join pieces of the bridge together in order for it to function as a single unit.    As for the Thunder Horse Platform, it is likely that it uses cables to secure it to the floor of the Gulf of Mexico.  It is a lot simpler and cheaper than building a huge structure that would tower above the floor of the ocean.

The trick would be in how to employ these techniques in outer space.

By the way, while reading Zubrin's novel, First Landing, I noted that in the story, there was this part about precious minerals on Mars.  I can't confirm this, but it would be a commercial incentive to go to Mars, provided that they exist there.  It is probably too expensive for private enterprise to launch rockets and such, but if some infrastructure could be put up there, it may become a reality some day.