How do I get from Puerto Ayora to Baltra Airport?
In Puerto Ayora, you can stop any taxi and ask the driver if they can take you to the Itabaca channel ("el canal Itabaca"). Taxis are are usually white pickup trucks, often Toyota HiLux or Nissan Frontier vehicles. They can accommodate up to 4 people who can all share the price - around $25.
From central Puerto Ayora to the channel is a 26 mile (42 km) trip up and over the Highlands of Santa Cruz and through the delightfully cool scalesia forest. Once at the channel, board a ferry or take a water taxi to cross over. Depending on when you arrive you may be able to catch the ferry operated by the city government, which costs $1 per person. The private ferry boat costs $2 per person. Bags get stowed on top of the ferry, passengers go inside.
Once you arrive at the other side of the channel you can board an airline bus direct to the airport terminal. The ride costs 5$ per person. Baggage is stowed in the locker below and you climb aboard. Note that these buses are always very crowded, but the journey time to Baltra airport is less than 10 minutes, so don't worry.