It is technically possible to fly both ways for negative $4 if you’re up for a really long vacation: Fort Lauderdale to Aguadilla, Puerto Rico from 9/30-12/02 comes up to $36 RT after all taxes. Otherwise it’s primarily only good for the one-way, but round-trip travel is required.
Also be prepared to be nickeled and dimed for everything from checked luggage($5-$10/bag) to lap infants($25) to a can of coke($2).
Remember to unselect the $9 fare club and the $12 travel insurance which Spirit tries to sell you by default when you buy a ticket!
HT: Eli W.