Brian is completely right in that a decent paint will help.  A lot of craft stores now, like Micheal's and/or AC Moore carry a line of Badger Airbrush paints.  Badger paints are great.  I have a couple of the weathering type sets and they give a nice coverage.  The cost is low too.  Probably, you could pick up a small set for under $20USD and online they are about that too.  Then build up your stash as you go. ;D