Here's a great source for air bags.
http://www.airbagit.com/

If you get one of the buy 2 get 2 free deals you can get them for less then $37 each with shipping included
http://www.airbagit.com/SearchResult...arch=free+bags

Oh, and they have good valves for air cannons too
http://www.airbagit.com/v/vspfiles/p...lves_PAGE.html