> I don't know what technology could get a ticket to Mars from the Earth down to say $100 USD,
I do, but then I wrote a textbook about space systems engineering [ http://en.wikibooks.org/wiki/S... ]. It's a combination of self-replicating automation, extracting local materials and energy everywhere, and a space elevator network.
* It would be very expensive to haul all the equipment you need to Mars in order to live there. Instead, what you want to send is a starter kit of basic machines, and use those to build other machines, until you grow big enough to make the final equipment (habitat domes, etc.). You prefer to make this starter kit as automated as possible, since you won't have the facilities to support people until later. You start on Earth, and build a starter kit that grows to a full factory. That factory builds a second starter kit that gets launched to orbit, where it grows to a full factory. In turn that one sends a starter kit to Phobos, and then finally the Phobos one sends one down to Mars.
* All of the factories run off of local solar energy and process local materials to make most of the new products. A few percent will need to be imported parts, because they are too hard to make, or use rare elements. At each location you build up greenhouses, habitat modules, and processing plants. One of the locations is a "Cycling Mars Transfer Orbit", which goes back and forth from Earth to Mars. So instead of sending 10,000 Mars Colonial Transports carrying 100 people each, you build up a mining colony/transit hub that makes multiple trips, carrying people each time.
* A rotating elevator (Skyhook or Rotovator) can provide about as much velocity change as a rocket stage. A series of them in Low Earth Orbit, High Earth Orbit, and Mars Orbit can provide the velocity changes to hook up with the mobile mining colony, and then put you down on Mars.
Such a system would be low cost to build and run, but you need enough traffic (like 10,000 passengers a year) to justify building it.