Airbrushing is a big topic, full of opinions and there is simply no way I can cover all the aspects of airbrushing in this post. I've owned 3 airbrushes since March 2012 and I've learned a bucket load in that time, but still have plenty left to learn.
Airbrushing the early days
I started airbrushing by purchasing one of those cheap Chinese kits you can get from eBay. Now most airbrush artists will tell you not to get one. My opinion, this is a great place to start and I'm very glad I did. First off you may find you don't like airbrushing, that it isn't for you. It's a steep learning curve and this can put people off. Please don't think you can pick up an airbrush and start knocking out awesome looking freehand camo stripes because you've seen some youtube videos and it looks easy. Back to the Chinese copy...I spent about £80. I got a compressor, it lasted about 2 years and I ended up donating to my FLGS along with the hose and of course I got a gravity fed, dual action airbrush which suffered a tonne of abuse at my hands for about a year.
Since then I've learned a thing or two, I now know that I should have gone for a kit which had a compressor piggy backing a tank and have gone for a single 0.3mm needle and nozzle. This experience was put to good use when Adam's wonderful wife asked for my help in buying him his first airbrush as a present. As far as I know, Adam's put that thing through its paces and it's still going strong. I've just had a quick look on eBay and you're looking at £65 for similar setup, that my friends is a bargin.