It is best to arrive in Juan Santamaría Airport in the capital city, San José.
1. You can fly from San José via (SANSA CR, NATURE AIR) to Quepos ($75 p.p)
You can rent a 4 wheel drive in Quepos Airport.
2. Rent a 4 wheel drive in the Airport, then drive from San José to Cerro Nara, with takes 4 hrs.
(A simple 4 WD is Jimmy Suzuki, $60 / day. 4 passengers.)