The airport on Isla San Cristóbal is situated less than a km from Puerto Baquerizo Moreno. There are three airlines flying to San Cristobal from the mainland and they are TAME, Aerogal and LAN. There are also small planes flying from Isla Baltra and Isla Santa Cruz.
I did not arrive to San Cristóbal by plane but went to the airport to change the date of my return to the mainland (from Isla Baltra). I changed at TAMEs counter at the airport. When I first arrived they were busy with check-in and I was told to come back a little later, when the planes had left, so I went to have lunch first. It only takes a few minutes to walk to Puerto Baquerizo Moreno so I walked. A taxi would have cost $1.
The airport on San Cristobal is very small. When I visited in July 2013 there were some construction work going on so it will probably look different if I ever come back.
Speedboat between Puerto Ayora and San Cristobal
On my previous visit to Galapagos Islands I had heard it was good to purchase the tickets for the speedboats one day ahead of departure. Therefore I had planned to stay in Puerto Ayora one night after the cruise before going to San Cristóbal. I changed my plans and hoped there would be a ticket available on the same day I had arrived back to Isla Baltra from a cruise. The bus from the canal stopped just opposite the office of Cobomar, where I had bought a ticket for Isabella two years previous. There was no problem to get a ticket for the boat leaving at 14.00. Besides the speed boat leaving at 14.00 there were now speedboats leaving for San Cristobal and Isabela at 7.00 too. A one-way ticket was $30 (July 2013).
There were several hours left until the boat was leaving so I left my luggage at the office of Cobomar and went out to do a few things in Puerto Ayora. I came back in good time to pick up my luggage as all luggages have to be checked on the pier. You are not allowed to bring seeds and fruits between the islands, so there is a control before you travel.
The speedboats to San Cristóbal and Isabela are leaving from the pier in Puerto Ayora. To the speedboat we had to take a water taxi, which we paid $0.50 for. On the boat there were lifejackets for everyone on the boat and we were told to wear them during the journey. The journey between Puerto Ayora (Isla Santa Cruz) and Puerto Baquerizo Moreno (Isla San Cristóbal) took 2h.
I stayed on San Cristóbal several days. The day before it was time to go back to Puerto Ayora I bought a ticket from one of the agencies along Av Charles Darwin. It was $30. The boat left from the pier in Puerto Baquerizo Moreno at 7.00. I was at the pier well in advance as also here the luggage is inspected. The journey to Puerto Ayora took around 2h.