So you can go to Costa Rica if you have a return air ticket with a date within 90 days. Then you can renew your visa by going to Panama and coming back - and you can use your return bus ticket as your new 'visa'.
Can you then change your return flight date, so that it's still good? How long can you postpone that return flight? How many times? Only on certain airlines?
Jason Holland - Roving Latin America Correspondent
When first flying to Costa Rica you should have return air ticket within 90 days of your arrival. That gives you a 90-day tourist visa. You can renew the visa by traveling to the land border with Panama or Nicaragua. In that case you can use a bus ticket out of Costa Rica as proof you are leaving the country within 90 days.
But you don't need to have bus ticket. If you had a plane ticket showing you were leaving within 90 days that would work too. One way to keep reusing as a plane ticket is to buy refundable ticket and the switch the date of the return flight as needed. But keep in mind that to do that you need to buy refundable ticket, which tends to be more expensive and there is usually a fee to change the date on the return flight.
I would refer you to call the indiivual airlines to find out their policies on refundable tickets.