I have 3 airbrushes.. all bought from Ebay. 2 are from China and one is australian.
The Chinese ones are bloody great... the Aus one played up after a short while.
For painting.. make sure you get one with a .5mm nozzle... you can use .3mm but it doesnt allow heavy flow when you want it ( you can always move your needle up a .5mm to reduce flow).
Make sure its a dual flow and gravity fed is much better for touch ups.... a syphon feed with jar and nozzle open full bore can CC a PF no problems and allows you to apply thicker in areas of heavy wear. I like this method as it doesnt give the big thick coating effect a standard sprayer would.
Airbrush gives heavy up the shooter and ball arch, round bumpers etc but light in the centre... gives a CC that doesnt look like a sheet of glass on the PF.
Another tip is to buy yourself an airflow adjuster that sits between your airline and the brush.... allows fine airflow tuning... these are essential!
Oh and never drop your needle.. f**ks em up big time