The island is small enough that unless you want to go to Puerto Chino, El Junco or La Galapaguera for the day or don't feel like hiking to El Progreso, you can walk wherever you need to be. From one end to the other Puerto Baquerizo Moreno is about a 20-30 minute walk.
If you don't feel like walking, hail a taxi hold your hand out, palm sideways and point your arm towards the ground. It should be $1 anywhere in town including the airport. El Progreso, Puerto Chino, La Galapaguera, and El Junco cost more and official prices have been established by the local government, check the board on the Tourist Pier for information on costs to these places. Since official prices have been established, no additional tax are allowed and Ecuadorians and foreigners are charged the same.