In 2018 I took advantage of Frontier Airlines $80 round trip flights from Las Vegas to Miami for a trip to Key West. Sure they charge for seats and bags, but I traveled with only a backpack under seat carry-on and took a random seat assignment. The round trip ticket price was $80 all-in to fly to Florida for a vacation trip in January.
Frontier Airlines has a $79 round trip ticket for San Francisco to Miami with a couple of November departure dates, Nov 16 and 18, at the time of this post with more $39.50 one way dates for MIA to SFO.
Frontier Airlines San Francisco SFO – Atlanta ATL – Miami MIA – ATL – SFO