Costa Rica has a useful twist for travelers who don't know their return date: its official tourism guidance explicitly recognizes commercial bus tickets as one form of onward-travel evidence. That opens the door to a classic Central America route—fly into San José, spend time on the Pacific coast, then continue toward Nicaragua or Panama—without necessarily buying a flight home.
The key is not choosing the cheapest-looking document. It's choosing an exit arrangement that matches your actual route, your permitted stay and the form of transport Costa Rica recognizes.
What Costa Rica actually asks to see
The Costa Rica Tourism Board says visitors must have a return or onward ticket and proof they will leave before their permitted stay ends. Its guidance specifically flags travelers arriving on a one-way ticket, travelers with a return flight more than 90 days after arrival, and people who fly into Costa Rica but plan to fly out of another country.