According to U.S. News Travel, it is possible to get a domestic, round-trip flight for as little as 10,000 miles. Each airline differs, and most airlines have a variety of ways to earn miles. Flying frequently is the most common.
Certain credit cards, hotels and other services have deals with airlines that allow travelers to earn miles in ways other than flying. These deals usually allow members to turn all or some of their dollars spent into miles for the purpose of frequent flier programs. By using these deals, it is possible to have a person's first flight lifetime be totally free or to have part of the 10,000 miles come from some source other than actual miles flown.