immigration law in CR

This  proposed 'law' was suspended until next year.

Yes, your airline ticket must be less than 90 days.

No, you can only pay the mentioned fine in San Jose, if you are from some countries that have a 30 days visa. You have to exit the country, but it's not necessary to stay out 72 hours, then return showing a ticket out of the country.

Residency information

I'm not 100% sure but I don't think it's a good idea to "just pay the fine" instead of actually leaving Costa Rica for a few minutes and coming back in to renew your 90 day visa. Maybe you could do it once, but not regularly. Again, I'm not sure but I think someone told me this.

What we've done is buy a plane ticket on expedia or wherever they allow cancellations within 24 hours...
Buy the ticket onward from Costa Rica to anywhere you choose, the night before you make your border run to Panama (I'd not recommend Nicaragua at this time due to political problems!! )(09-22-18) Print it out to show the border official if asked. (They don't always ask.)

After you cross over to Panama and then come back (should be no time limit required for your stay in Panama... BUT some border officials in Nicaragua when I used to go there would tell us we HAD to stay at least 2 hours in Nicaragua. I think this is illegal but you can't really argue with border officials...)

Anyway so theoretically you can cross into Panama, then turn around and come right back to Costa Rica with a new 90 day stamp. NOTE ALSO that they don't HAVE to give you a 90 day stamp. Check to see what they gave you before you leave the official who stamped it. MAYBE you could convince him to make it 90 instead of 30...? Usually it IS 90 days, but one never knows...

Once you get back into Costa Rica, go on expedia and cancel the flight within the 24 hours since the time you purchased it; they have a button for that. "CANCEL" I think it says.  Your money is usually returned to you within 24 hours as I recall.

Thus you don't have to buy a non-refundable bus ticket or go anywhere to do anything to get a required return ticket to Costa Rica.

Just be sure to print your forward ticket out of Costa Rica ticket info, and MAKE SURE You do cancel within 24 hours, and make sure your flight is cancel-able within 24 hours.

(I'm not sure but I think that in the U.S. all airlines HAVE to allow a cancellation within 24 hours...? I always used Delta for this, never had a problem. By the way I'd always buy the cheapest ticket out of Costa Rica I could find "just in case" I didn't get my refund. But I always did get the refund. Many people use this "trick" to get the required onward ticket when coming back in to Costa Rica.