I recently started airbrushing as well and went through the same thing figuring out what I needed and what I should buy. Some of the things that affected my decision were would airbrushing yield better results than the methods I was currently using, would I like using the airbrush and want to continue, and what type of airbrush would feel the most comfortable.
In the end I settled for 3 different $25 airbrushes. Dual action gravity and siphon, and single action siphon. I have to say I think I made a good choice. All three airbrushes work great and now I know first, I really like airbrushing and its effects and second, dual action gravity feed is my favorite!
I'm quite thankful I didn't buy $50 or $100 airbrushes since now two of them are just going to collect dust on my shelf. I see the advice other posted about $=quality, but as far as my newbie knowledge goes (not far, I know!
) all the signs of quality are there with my cheapo airbrush - no sputtering, even consistent flow and nice smooth lines.
That said, their advice is very good!
Getting proven quality will eliminate the chance of bad equipment affecting your experience.
In the end I recommend grabbing some cheap ones and playing around with them. When you've decided if you want to continue and what kind of airbrush you prefer, then go get one of the high quality ones.