Spirit has been expanding like crazy into Latin America. I'm planning a long trip to Central America at the end of October. I'm retired, so I like to fly somewhere travel overland, then fly back to the US from wherever I end up.
I started out, though by mistake, pulling up round trip fares, and I didn't think they were good at all. The one way fares, however, were really good. I think a couple of them were less than I was getting for round trip.
It's a good new option to places that, although close, usually cost a fortune to reach.