Jaco itself does not have an airport, the closet one is Quepos which is serviced from San Jose via
www.natureair.com and
www.taca.com (regional SANSA operation). Quepos isn't very close to Jaco and unfortunately has a one lane bridge inbetween the two which can take upto an hour to cross (sometimes longer).
The only other alternative it to hire a private helicopter to shuttle you from San Jose's Juan Santamaria Airport (SJO) or Pava's Airport outside of Rhomoser to one of Jaco's make shift helipads. Last time I checked The White House Hotel (
http://www.whitehousecostarica.com/ ) in Escazu, San Jose also had a new service with it's private helipad out to the Los Suenos area of Playa Herradura, which isn't too far from Jaco.
Hope this helps
Jim