Schmincke Opak and Createx Classic Opak Schmincke Colors are nice for paper, use that a lot for my training,runs well without thinning, self whit an 1.5mm setup Createx use i for differend undergrounds
Believe me, I tried cheaper paints and it's a false economy.
With inferior paints you will always have trouble with things like clogging, tip dry, thinning to get the right viscosity just to get it to spray and the list goes on. Not only is this a waste of your time (time=$ ) but you waste a lot of paint in the process by test spraying to clear your ab, emptying to clean etc. All a very frustrating experience and will not help with your progress to get better.
The better quality paints spray a lot easier, have finer pigments made specifically for airbrushes and usually have better covering qualities, less problems and the result is you use a lot less paint.
If really you want to use something cheap just to get your strokes down I've heard of people using inks to practice with, these would most likely give you a lot less trouble.
Ah ok, you are using the 'fluids' line of paints, seems you might need the ab medium as well. I'd try with water first and if the paint sprays out ok it will be fine for practicing. It becomes more important to use the right extenders and reducers when you are doing work for customers as you don't want them coming back complaining thier new paint job is falling off
A qucik snippet from the Golden site: http://www.goldenpaints.com/products/color/airbrush/airbru1.php
GOLDEN also produces other full lines of acrylic paints, including Heavy Body, Matte, Fluid and High Load Acrylics, that are compatible with the Airbrush Colors. These products can be used in conjunction with the Airbrush Colors to combine the effects of spraying with those of other application techniques, while working with the same color. When mixed with Golden Airbrush Medium, the Fluid Acrylics perform very well for airbrushing, offering the artist still further choices in color selection