Scott,
Where are you, man?
I know quite a few places in Melbourne where you can get a good airbrush at a good price.
Is this a help for you?
I've never used an Aztek - I use a very old Badger single action, internal mix - similar to the current model 200NH. It's really a very good airbrush - with fine, medium, and heavy tips and needles, it's lasted me for over 20 years with very good results. It's easy to use and easy to clean.
I also have another Badger, a model 150, a double action spray gun. It's more complicated and takes practice to master, but it's also a really nice tool to use.
Have a look around and find arts supply stores, hobby shops, and also try the student union bookshop of your local University. I've recently completed my uni time and got heaps of stuff pretty cheap with my student discount when I was a student.
Let me know where you are and I'll look around for you.
Cheers,
LeeTree