I assume you haven't heard from anyone else on a possible tour. I posted a message on Cruise Critic and got one reply. Basic text follows:
"We were on Mercury last Jan. and arranged our own tour in Puerto Montt through Travel Sur Chile. The price for 4 was $120. We went to Petrohue Falls. It was great to be there in a small group. As we left, the masses of people from ship were arriving. We think we got pretty much the same for $30/each. Our tour guide, Barbara, was great."
So, I am going to email them and see what they say. Would you be interested in doing this tour with just the 4 of us? Carol