The old adage of "You get what you pay for" usually holds true, especially in airbrushes.
The quality and standards of the Harbor Freight airbrushes are bad at best. They buy their brushes from who ever is selling them the cheapest that week. You can't get replacement parts, and the brush you buy next week may be completely different than the one you bought last week. If you don't know how to airbrush then you are going to be spending some time airbrushing long before you attach your car or project, and the skill doesn't come overnight. Don't get me wrong, I'm not trying to scare you away from airbrushing, I'm just pointing out that damage and loss of parts often come during the learning process, so getting replacement parts is often a necessity.
I'd look for or at a Grex or Iwata airbrush, and for someone who hasn't airbrushed before I'd probably look at their gun style trigger models. They're easier to learn with. For doing murals or surfaces that will be at extreme angles I'd look at a side feed rather than a top mounted gravity feed. Side feed brushes allow you to rotate the fluid reservoir to any angle, they also allow you to use a larger reservoir/paint cup. That's a big deal if you are going to be spraying much in the way of volume/big areas at one time. Otherwise you end up refilling a tiny reservoir every minute or so.
I think that you will find that after you have learned to airbrush and finished your job that you will want to hold onto your brush, if not you can sell it on ebay, craig's list, etc. and recover most of your money. Keep all of the paperwork, the original box and packaging, and keep the airbrush clean. Clean brushes with all of their original materials and packaging do better in sales, than loose, dirty brushes.