Keith's note: So what would this Dragon 2 mission to Mars cost? SpaceX would use a Falcon Heavy which they sell for $90 million. Of course it costs SpaceX a lot less to make the rocket than what they sell it for. Also, SpaceX is starting to build up an inventory of used first stages that they put into rockets and sell for something like 30-40% less than a new Falcon. Of course, they make a profit on these reused Falcons too. Conceivably they could build a Dragon Heavy for Mars mission use out of used Falcon first stages. Of course there's the cost of a Mars-capable Dragon V2 (aka "Red Dragon")that has to be developed and built. But by then they will have some Dragon V2 vehicles sitting around as well. Then again SpaceX could use all new hardware. With an increased launch cadence there's going to be a lot of these stages sitting in storage making subsequent missions less expensive as well.
My point? This private Mars mission business is not going to be as expensive as some of the SpaceX doubters would have you think - especially if they also start to sell payload space for science instruments. And given the multi-billion dollar cost schemes NASA floats about how it would do sample return missions, one would have to expect that a SpaceX Mars architecture could slash the cost and complexity such that it would be in NASA's best interest to invest. Depending on who you talk to a lot of people would like to have the Mars sample return thing done before humans ever get sent to Mars (e.g. answering the life on Mars question). NASA has a slow-motion, multi-decadal "plan" for sending humans to Mars. What is the value of accelerating the pace at which preliminary things such as sample return and large propulsive landing technology? Answer: billions of dollars and many years.
As some of these articles above start to consider, is there an actual market that investors might start to consider that involves doing things on Mars? The answer is yes since SpaceX just decided to start spending their own money on it.