Southwest is celebrating their big 50th anniversary today with round-trip flights from Denver (DEN) to San Juan, Puerto Rico or San Jose, Costa Rica (SJU/SJO) for $208-$279. $104-$157 each-way. Flights September 15th to November 3rd. Origin/Destination reversible.
You may need to enter the “SAVE50” coupon-code during your search to see the fares, but so far, all fares seem to show up without the code.
Southwest doesn’t charge a fee for changes, cancellations, or carry-on bags.