When traveling to Costa Rica with more than US$10,000 in cash or its equivalent in colones or euros, nothing happens as long as you declare it on your customs form upon landing. The same applies to land and maritime borders.
Customs officials may, however, want to know the reason. Kinda depends on how much more than US$10,000 and even where you are coming from.
What do you do? What are you planning to do with the money? could be among the questions. But if you enter the country (any country) with an exuberant amount of cash, officials will dig further.
Not declaring the cash has it consequences. Such as the case of a foreigner surnamed Suárez Vargas, arrested last Thursday (September 28), at the Juan Santamaría International Airport (SJO), with US$27,100 dollars when he entered the country on a flight from Mexico
Suárez Vargas did not declare the cash and will now be spending the next three months as guests of the country (preventive detention), while the Deputy Prosecutor of Alajuela investigates the case of alleged money laundering.
— Seguridad Pública (@seguridadcrc) September 28, 2018
The man was detained by the Policia Control de Drogas (PCD) – Drug Control Police, with the use of a police dog that detected the cash in his luggage. Apparently, the money had traces of non-illicit substances.