There are two domestic airlines: SANSA and Travelair. Demand for seats is high, so try to book as far in advance as possible. The majority of Costa Ricans do not own cars, so public transportation is quite well developed, although connections between towns other than san Jose are limited. Most multi-destination trips will require backtracking into San Jose and then catching another bus outward again.
The buses are not that comfortable and to the uninitiated and faint-of-heart the system can seem incredibly chaotic, but ask any Costa Rican for advice and they'll point you in the right direction. The good news is that the fares are generally cheap - no destination is more than US$7 away. There are three major bus depots: the Coca-Cola depot about a 20min-walk east from the city center, down Avenidas 1; the newish but understated AtlÃ