Realistically expect what you consider "affordable".
Carefully online monitor major airlines for the flight date/time you seek; you may note that every 15 to 30 minutes, you MAY see flight rates come up or down; a matter of finding what you seek, at the right time.
Have ready the following: Credit card info, a note pad / pen ( so you can compare competing rates )
Just beware, finding that perfect "cheap" rate might mean some serious sacrifices, like comfortable seating space--passenger "cramming" is popular within the U.S. airline industry right now; thank Spirit Airlines for that one, they started the practice.
Also factor in luggage weight variables; that s an understandably big concern with airlines.
And check out the ever-popular TSA website to see what passengers are allowed--and NOT allowed--to board with.