You'll have to move quickly to take advantage of Frontier Airline's latest flash sale. Until midnight on February 5, you can find $29 one-way flights around the US. Even if you find the sale too late, the airline is bound to have cheap flights available. That's kind of the thing it does.
There are cheap sojourns available over short distances, but there are deals just about anywhere the airline flies. A total of 38 routes currently have flights under $30.
If you happen to be a member of the airline's Discount Den club, you can get the cost down as low as $19 per one-way flight. At $49.99 per year, it may make sense if you fly with budget airlines regularly. It would only take a couple flights (or one flight with multiple tickets) to see the membership pay for itself.