Costa Rica's largest airport is in San Jose (SJO) which is roughly a four to five hour drive to/from Nosara. If you do not want to make the drive from San Jose you can take a national flight from SJO to Nosara. Schedules and costs vary depending on time of year.
The closest international airport is in Liberia (LIR). Liberia only opened in 2004 and we have seen new flights every year. Liberia is about a 2.5 hour drive from Nosara. Domestic flights are also available from LIR to Nosara. Schedules and costs vary depending on time of year.