The old saying you get what you pay for holds true with all types of tools. A cheap airbrush won't have the spit and polish that a good one will, and it might never become evident to the person if they give up.
A well machined and polished brush, needle and nozzle will allow the paint to flow through the brush smoothly, and cause less problems, parts will be easy to find, and won't be so problematic to find that purchasing a new brush will actually be cheaper than replacement parts. There's a thread recently where a guy wanted to find a needle for an off brand brush, $16 plus $10 shipping. It's good practice to replace the nozzle as well, further adding to the cost of retooling his brush, which was an off-brand to start with. Had he bought a name brand off the line, he would have spent the same money, and almost any hobby or art shop would have replacement parts.
My recommendation would be to get a Sunday paper, and find the Michael's or similar craft store (if you have one local) coupon, there's always a 40% off one item, sometimes a 50% off, and get the nicest model they have, which is generally a Badger, Omni or Paasche. You'll have a quality brush that you can find spare parts for locally, and will last forever if maintained correctly, and while their prices are higher off the bat, the coupon more than makes up for it.
That being said, I do like my Iwata brushes, but this site is living testament that it's the knucklehead holding the brush, not the brush itself that does much of anything, providing you get a quality tool.