I'm glad the info helps. I'm sorry; I forget how much they cost per day. I'm pretty sure it was the same at both places. The good and the "less good," shall we say. You can rent them by the half day too.
I cannot remember if they had brazons for water-bottle cages. I figure they must (?) -- at least for one cage? They are Treks. They don't have rear racks. I recommend a hydration system (like a Camelback) if you have one. Please take LOTS of water!!!! You can probably e mail K2 Expediciones from their web site: http://k2expediciones.wordpress.com/ and ask them all of your questions (price, water bottle cages, Valley of the Moon, etc.).
Valle de la Luna (Valley of the Moon) is fairly close. I don't know how long it will take you, but the bike shop (at K2 Expeditions) can tell you. That's a common bike trip. We already had it set up for a bus tour, or we would have gone there by bike.
I made a separate page for cycling San Pedro de Atacama on my Chile blog: paulajhunt.wordpress.com/cycling-san-pedro/ . It includes a lot of the details already mentioned in my earlier post.