I posted this almost a year ago. Here it is again. You may want to check the SJO website to look for any changes.
The branch at the airport is on the upper (departure) level of the terminal.
There is also a Bank of San Jose (BAC) ATM near the baggage belts down in the arrival level.
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From the SJO airport's website >>>>>>>
Bac San José
Phone: (506) 2295-9797 /
Web site:
https://www.bac.net/Location: Lobby
Open: 5 a.m. to 8 p.m
BAC Rapibanco Airport, located in the Terminal’s lobby, provides banking services for travelers. Customers can cash checks; make deposits; make cash withdrawals in colones, dollars and euros; pay utility bills and credit cards; and purchase travel insurance, among other services offered.
The BAC Rapibanco Airport branch operates 365 days a year, from 5:00 a.m. to 8:00 p.m. Its service platform consists of four service windows, an ATM and an electronic information kiosk.