My first was a Paasche H single action (the trigger adjust airflow, turning the nozzle adjusts the paint flow) for $45 in 1982. I was able to get very tight unmasked likes and very smooth finishes with it. until I misused it allowing the nozzle assembly to sit it thinner until it dried out.
My first double action (the trigger adjusts airflow and paint) was a Paashe VL I got at a hobby shop closing auction in 1993. It still works fine. I picked up a Badger 100 at a yard sale about 8 years ago. That one is a bit more difficult to learn, but works well. I was using it yesterday. This weekend, I scored a Grex Tritium TG with a Grex compressor for a really good price.
Save to get an airbrush brand compressor (starting about $125). The cans cost about $10 each. I once used a whole can ona 1/72 A-4 Skyhawk. I've been using a Sears for over 20 years; it works great but is very loud. It was about $100 back when I got it.
Don't be tempted by the kits at Harbor Freight. The airbrush LOOKS like a Badger but it's terrible to use. The trigger constantly stuck , airflow stayed open, there is only one needle size, paint shot back into the body. The compressor lasted about 4 hours of use over three weeks. It routinely stopped working during a session then died dead. Since every part was completely proprietary, that rendered the airbrush useless as well.
Short advice, find a name brand (Paasche, Badger, Iwata, Grex, Testor Aztec -a couple friends really like theirs, etc.) that feels comfortable and smooth from an art or modeling oriented dealer who will be able to provide support after the sale, such as new needles because you will bend needle tips in cleaning. While not impossible, you can find good deals.
Also, Google the brush for online reviews before you buy.