Well the paintball tanks are sort of overpriced I think... the local paintball place wants $45 for a 20oz tank, same at can tire... I imagine walmart would be similar.
getting one of these, which is cheaper to fill (well, per pound of CO2, more in total), standard fittings, and should last for life.. Guess I'll do a writeup when I get it going, if there is any interest.
http://farm4.static.flickr.com/3224/...3391afcdbe.jpg