Check out your local Princess Auto for an air brush (Calgary has two locations). They start at $15.99 for a basic one and go up from there.
I have the following air brushes from them:
http://www.princessauto.com/pal/Pain...-Kit/8430050.p
http://www.princessauto.com/pal/Pain...rush/8527491.p
Both are pretty decent and work very nicely.
I haven't air brushed any paper models though.