Manfrotto 5 Section Compact Travel Monopods
The more sections in a monopod, the more collapsed the monopod can be. A 5 section Monopod has more sections to collapse and drop down it's minimum folded length. Manfrotto has a few new 5 section travel monopods that can collapse down to just over 15", making them some of the shortest on the market. It's fully expanded length up to 57". Unfortunately these new lightweight travel monopods are only rated to support cameras at 3.3 lbs, but for light weight Photography or Videography shooters, it should be released at only $25 dollars.
If you're looking for something that holds more beef for cheap, the Cullman 550 - 5 section Monopod with quick release locks, will support up to 18 lbs., collapses to 18" inches and extends to 59.8". Currently on back order on many websites, but for about $50 dollars, it's expected.