I live by the tried and true finance method of the international traveler: use no foreign transaction fee credit cards as much as possible and withdraw cash from a local ATM with a no fee ATM/Debit card. Since Costa Rica is both plastic-friendly and American Dollar friendly, you shouldn’t have issues converting anywhere in the country. Make sure you have some cash if you’re driving though, as toll booths don’t accept card, but will gladly accept Colons or Dollars.