Buses between Quepos and Manuel Antonio (US$0.55) depart roughly every 30 minutes from the main terminal between 7am and 7pm, and less frequently after 7:30pm.
A number of international car-rental companies, such as Budget, operate in Quepos; reserve ahead and reconfirm to guarantee availability.
Colectivo taxis run between Quepos and Manuel Antonio (US$1 for a short hop). A private taxi will cost a few thousand colones. Catch one at the taxi stand south of the market. The trip between Quepos and the park should cost about US$15.