Jacó is cheap if you sleep and eat inland and expensive the moment you book activities, which are priced in US dollars for a North American market.
Sleep one street back — this is the whole budget
Beachfront and Pastor Díaz rooms carry a clear premium over identical rooms two blocks inland, and the walk is under five minutes. Nothing else you decide here moves the daily total as much.
The beach costs nothing; the board is the variable
Playa Jacó is free, long and a beginner's beach; rental and lessons are the recurring cost, and renting by the week beats renting by the day if you are staying. Playa Hermosa next door is not a learner's wave, so do not economise by taking a cheap board down there.
Carara National Park is the cheap day out
SINAC charges non-resident adults USD 10 plus tax and children 2–12 USD 5 plus tax. Open 8:00–16:00 May to November and 7:00–16:00 December to April; the main entrance is two kilometres south of the Río Grande de Tárcoles bridge, which is on the bus route north, so you do not need a car or a tour.
Know the canopy prices before you walk into a tour office
Rainforest Adventures' Pacific park near Jacó publishes its rates: the aerial tram from USD 67.50, the Tranopy zip-line-and-tram combination from USD 84.38, the six-activity Adrenaline Junkie from USD 111.38. Street sellers on Pastor Díaz quote against these, so knowing them is the difference between a fair price and a bad one.
What a day costs
The free parts are real: the beach, the sunset, walking the strip. The knowable ones are Carara at USD 10 plus tax, and a canopy or tram day starting at USD 67.50 and climbing past USD 111. Between those, a casado in a soda behind the avenue is a few thousand colones and the same plate on the beachfront is not. Sleeping inland and eating in sodas keeps a day here modest; one booked activity doubles it.