Check out badger's website and look in the garage sale section. They had a dual action airbrush (left hand or right hand, creatively designated rh and lh) for $35. The right hand model has a rotatable side cup mounted on the right side, so you can easily see your work, as well as paint straight down. Your air supply will be an issue. One cheap way to go is to get a five gallon air tank, fill it with a loud compressor and then use a regulator to control the pressure at the brush. A water trap would be a good idea in this case.
As an alternative, you could buy a quiet aircompressor from Amazon with a tank for 90 or so, or try building one of these
http://www.schnauzerfaceminis.com/dir/showthread.php?tid=478Tcp global has a good site describing their products and kits, and they sell through Amazon.
If you're working out the technique you should practice on cardboard, trying to make consistent dots and even lines.
I found "airbrushtutor" and schnauzerfaceminis set of videos on youtube to be very helpful, but by there are many great videos available.
On the topic of priming through an airbrush, it works great on my badger patriot 105 airbrush, and on the very cheap dual action air brush that tcp global sent with my compressor. You just have to clean the airbrush immediately since the primer, a special paint designed to adhere very well to metal, will be trying to adhere to the insides of your airbrush, especially the nozzle and needle tip.
Edit: just saw this forum post that would provide an air supply on the very cheap, if you're interested in a low budget alternate air source that is refillable.
http://www.dakkadakka.com/dakkaforum/posts/list/530799.page