Tour companies charge huge sums PER DAY for the "privilege" of taking you there. But as of March this year (2016) you can go on your own if you have certain activites planned - see the official press release at
Not everybody speaks Spanish and has the gumption to go on their own, of course. In light of this new development I hope that the tour companies will lower their prices, by a lot, and very soon. Those prices in the high three and even in the fourthousands for a six-day tour (really only four days on the ground) are outrageous when you think how much (or how little) things really cost over there.