Pat,
Your not going to get a set up for $40.00, Cheapest method would be hit harbor freight tools and order a small compressor, that will run around 40 bucks, You can get air brushes there to start with, a dual action will be around 20 and the single one will be 10, not these will be fine for vehicles and so forth but will not perform like a good air brush and achieve pencil like line, but I use the 10 dollar ones for 90% of my custom work. You will also need a regulator, ( 10 bucks). Use Acrylics, as enamels will not work on figures. Testors acryl is pre thinned for use in the air brush as is so you don't need to reduce it, You can also use many types of automotive Acrylics, just mix according to directions and that will be fine. I can take pics of the compressor I used to use for my air brushing if you like.