I started with a Pachee H 12 years ago when I was 18. Then I moved on to a badger 200 or 300...then an Iwata double action. I used to spray thicker latex paints and always dealt with airbrushes being clogged. When using good acrylics though I never had an issue either way. My idea for thick paints was to use the double action badger to apply basecoats and then do shading, lines, and delicate stuff with the expensive Iwata. These days when painting a latex mask with thick latex paints I use a brush for base coats and then airbrush with FW inks as they can thinned out a ton. They're really great paints.
Obviously with a Fett helmet you just need a working airbrush that applies nice and even coats and is consistent. Just make sure to invest in a decent capacity compressor as that can make a world of difference. The hobby or art shop desk compressors are loud and don't hold enough air to work quietly in my opinion and that's important when I'm in my studio/collection room and have a sleeping newborn down the hall in his bedroom.
Best advice I can give you is to always keep your airbrush perfectly cleaned in between uses. Nothing will wear your airbrush down faster and ruin needle tips and bottles worse than leaving paint in from the night before or just not doing a strict cleaning.
Lastly, monstermakers.com sells a quick change airbrush for applying colors fast and even supposedly without having to clean in between colors. I believe it's $20 or less but I haven't tried it out yet. Of course you get what you pay for but you don't have to go nuts. Check craigslist for a used compressor. Rather than spend $300-500 on a new compressor when mine died, I paid $50 for one that the person barely used at all and just wanted to sell it quick.
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It might be worth getting a good compressor and a cheap brush at first to learn the basics. Then you step up to a better brush. That's cheaper than getting a new compressor as well once you want to get serious.
I agree. Honestly, an airbrush is only as good as the person using it. No sense in going out and buying some expensive Iwata at first if you have no clue how to apply the paint correctly using it. Though there's a difference between just needing to apply even coats of colors and actually having to do layered detail work with thinned inks (veins, stippling, mottling, etc.).
I've even heard of people using automotive spray guns from hardware stores for their props that need quick even basecoats.