Allegiant Airlines is having a sale to/from Florida. The sale ends on May 10, and travel is through August 31. Fares from from $39 to $109 each way on nonstop flights. There is no round-trip purchase requirement.
In addition, as of this posting, Allegiant has several $19 one-way fares to Florida for a few dates in May. In some cases, these fares are only in one direction but can be combined with higher fares.
Keep in mind that Allegiant has a poorly disclosed "convenience fee" of $11.50 per passenger. That includes booking online. If you book by phone, there is a $10.50 fee per ticket.