For as little as $39 one way, you can fly from Tampa-St. Petersburg airport in Florida to the Tri-Cities in Tennessee. This amazing fare is being offered by Allegiant Airlines (www.allegiantair.com,) a low-cost carrier.
Fares from Tampa to Niagara Falls NY start at $68 one way, and to Plattsburgh NY at $89. These airports attract a lot of Canadians who are willing to cross the border to enjoy much lower air fares.
I have flown once with Allegiant and found the flight was fine. I did encounter some problems once on the ground in Plattsburgh, NY but they were not related to the airline.
However, the airports Allegiant uses are not the largest ones, and it may cost more to get there. In addition, if there is any problem with a flight it may take a long time to get a replacement aircraft.