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.
Cheers,
Mick.