Return ticket, any practical solution?

Hi everyone. Im flying from Medellin, Colombia to Belize next week. So again I have to jump through hoops with the return ticket issue. I never plan ahead very far, so I have no idea where I'm going after Belize, or what date I will leave.

I called the airline and they say a ticket out of Belize is required, but it doesn't have to be an air ticket.

So I'm desperately trying to book some bus out of Belize, for example to Cancun, but without any luck because ADO doesn't even list international buses on their web site. And if they did, I've heard from others it cant be purchased online without a Mexican credit card.

Any of you have a tip on what I should do to get into Belize?

Other times I have just bought a refundable air ticket out of the country, but that turns out to be a huge headache because some airlines have an unofficial policy of never paying that money back, for example Avianca. Officially it is refundable, however it is like pulling nails to actually get that money.

So I usually end up buying an air ticket that I later throw away, and that's sad loss of $300.

BTW, this is not an Immigration Authority issue, it is an airline issue. The airlines force this on people. If airlines are so scared of letting people on board that the receiving country might reject, why dont they allow us to deposit $500 in cash at check-in, which we then can withdraw at their ticketing counter of the arrival airport? Or IATA could have a service where you could deposit $500 which could be claimed by any airline worldwide when they have to return a person that was refused through immigration.