Air Brush Necessities
There are many types of airbrushes and compressors out there. Any airbrush you buy from a chain Hobby Store (ie Michaels or Hobby Lobby) is probably going to be grossly overpriced. The most basic air brush can be bought at around $50. You can get more fancy air brushes that have more control over the PSI at finger tip level and a wide range of needles among other things, but I haven't seen any of that as a necessity so far.
My personal air brush is a Paasche H Model. It comes with three needle sizes and is a single action airbrush meaning it turns on and off. You can find them on Amazon or eBay for $40+ (or straight from Paasche for much more).
The air compressor is the other main component. They start at around $70 depending on where you go and what kind you get. The compressor I have was given to me by a family friend and is a Paasche from about 1970 or so. It still works perfect despite its age. The compressor you get should pump out a max of 40-50 PSI. Optimal PSI for airbrushing varies from 25-40. The higher the PSI the finer the paint particles are, the lower the PSI the bigger the paint particles are. I leave my PSI around 30 but adjust it based on paint thickness.
The Master Airbrush compressor looks like a good choice for $70 on Amazon. I do not personally have one but it seems to be highly rated. I encourage you to shop around and see what you can find.
Most airbrush compressors come standard with an air regulator with filter and water trap. This device gives you a constant stream of pressure and is adjustable with a dial. It also filters out dust and water from entering your air stream.
If your compressor does not have one, or you buy a compressor not necessarily made for airbrushing, you can pick them up at most hardware stores or on Amazon.
Thinner is very important if you plan to be buying paints that are not pre-thinned. Each paint type has its own thinner and each company seems to have their own thinner for their own paint. Acrylic thinner is a mixture of water and binding agents. Enamel thinner is made primarily of 'mineral spirits'. It's a type of oil reducer that breaks down oil into a liquid, taking the clumps of enamel paint into something you can spray. Realistically you could pick up a big gallon of regular mineral spirits from your hardware store, or any other type of oil based paint thinner. However, airbrush paint thinner (both water and oil based) usually contain some other chemicals to help with panting and binding. For this reason, and to play it safe, I try to buy the same brand thinner as paint or atleast airbrush thinner. My prefered thinner for both enamel and acrylic is Humbrol as I primarily paint in Humbrol. This, however, can be hard to get in a pinch in the States and is often out of stock on their website. For this reason I use Testors Universal Enamel Thinner for enamel and Createx Transparent Base for acrylic.
You're gonna need jars. A lot of jars. Think you have enough? You don't. Every color, every mix, and every brand of paint gets it own jar. Throwing out unused paint doesn't make much sense so I never get to reuse a jar.
Glass airbrush jars are the best thing to keep mixed/thinned paint in. They are also what will connect to your airbrush. I have bought several sets of these airbrush jars from Amazon. They work great and hold one can of Humbrol paint with thinner. Larger jars are also good to have on hand for mixing paints together. I was given a few dozen larger glass jars for this reason. However, any glass jar will work for mixing and storing paint.
Jars with siphons expose the paint to air. This causes paint to dry out during storage. I recommend picking up some jar nubs to keep paint from drying out. You'll have to put tape on the hole on the lid of the jar too.
A paint mixer/stirring tool is the best quality of life improvement you can buy. I used popsicle sticks and plastic rods to mix for the longest time, then I discovered this. Put this in your paint, press the button, and watch it mix. All the liquids get mixed perfectly together without clumps and clogs. If you're going to me mixing, thinning, and storing - get this.