The cities with the cheapest flights include Atlanta, Austin, Charlotte, Cincinnati, Cleveland, Dallas, Denver, Detroit, Fort Lauderdale, Fort Meyers, Houston, Indianapolis, Kansas City, Las Vegas, Milwaukee, Minneapolis, Nashville, New York City, Omaha, Orlando, Philadelphia, Phoenix, Portland, Raleigh, Saint Louis, Salt Lake City, San Antonio, and Trenton.
However, make sure you understand the fees before you book. The airline charges a fee for checked baggage and will charge a fee for a full-size carry-on. Those fees vary based on what you're checking and when you're checking it. The carry-on fee is generally between $30-35 and the checked baggage fee is around $25 if you pay online at least 24 hours in advance of departure.
Additionally, the airline charges to reserve most seats. In the example above, one flight had seats you could reserve for free. With one checked bag and a seat reserved in one direction, the final price was $81.40, including taxes.
If you can deal with being assigned a seat (gasp) and wearing your clothes instead of packing them, this can be a cheap trip. (As with the example above, it can be cheap even if you don't put everything on and go to the airport puffed up like the Michelin Man.) Get a full picture of the cost before you book and then starting planning your summer vacation.