On another forum sometime ago I had asked if there was an airbrush sized in between what artists and modelers use and that which is typically used to paint a car or house. I got no reply. Well I was perusing Jerry's Artarama website some time ago and found this on clearance (about 20 usd):

Perfect size for modding or respraying cases and whatnot. I dug it out of my stash the other day, needs an adapter to connect to 1 of my compressors. Compressors aren't really expensive, an expense of nevertheless, you could get 1 for ~120 usd from the same source. There are ways of connectimg a garden sprayer, the type you pump up and down, if you're im disposed to buy 1 (in fact years ago I bought an adapter that attaches a airbrush to a tire).

Shop aroumd though. Don't immediately go to amazone.

I'll update this when I have it working.