The cheapest $20 flights are from Boston to New York City (JFK), Long Beach to Salt Lake City and San Francisco, New York City to Rochester, and Oakland to Long Beach.
There are also $30, $40, and $50 flights from Boston, New York City, Newark, Westchester County, Baltimore, Fort Lauderdale, West Palm Beach, Long Beach, and Oakland to various destinations.
The cheap flights are JetBlue's Blue fare, meaning checked baggage is not included.
As mentioned above, dates are very limited — but you could take a spontaneous trip to Savannah from New York City for $30 (return flights range from $78 to $255).
Traveling in November before Thanksgiving and in early December before the winter break are great ways to score a deal.
If JetBlue's most recent flash sale isn't tempting you, consider some of the cheap flights available to Hawaii this winter.