Remember, you can also pay in dollars at many places, and all the girls will accept them - some will tell you do everything in colonies, others a combination. To avoid currency losses, on the other end, exchange an amount that you think you might use.
I'm going for 15 years and what I do is exchange - at the BANK, upstairs across the street from luggage claim, customs - just walk across the street and go upstairs - its where the ticket counters are located - just past where you buy your exit stamp (do that now; get it done and one less thing to worry about) is the bank (BAC) - small, but you can't miss it.
I'd exchange what you need right them - b/c often hotels, casinos, will not give you the best rate, always seem to be out of small bills

and sometimes just don't have the change to exchange, especially larg(er) amounts of money.
Also, I don't want to be - from a time and safety standpoint, screwing around with going to a bank in San Jose, and carring money back to my hotel - far easier and better to get what you need at the airport bank and take it on a taxi to your hotel. While the airport bank is fairly quick, Costa Ricans have put up with bad [customer] service for so long its come to be expected, so what should be a simple transaction at at a downtown bank often takes longer than it should, another reason to exchange at the airport bank.
As everyone else has posted, never exchange in the USA; you are just getting screwed, although the 2 currency exchange booths at the airport do a pretty good job of screwing you too

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