I have been airbrushing crankbaits for a year with a cheap air brush from Harbor Freight.  I am looking into getting a more up scale one now that I am more advanced in painting.  I want to keep it under $100.  What brand is a good one to get?

I have the Iwata Neo, It's perfect for painting crankbaits.  Although I had to buy another after I broke my first one, because I didn't know how to properly clean it.  I think it was like $80.  But if you buy it from Hobby Lobby you can use a 40% off coupon, which it puts it around $50. 

In the $100 range i would look at the iwata eclipse cs. You can find it at hobby lobby with a 40% coupon or often at coast airbrush as a used classroom airbrush.

I would look into a "Copic" airbrush system.

 

No mixing of paints, no mess, just use a marker style cartridge. It is what I will getting herre soon for some things I want to touch up.

 

http://www.amazon.com/Copic-Air-Brush-System-Kit/dp/B001398KDQ

I've painted cranks for more than a decade and have used various airbrushes.  My favorite, which is easily within your budget is the Iwata Revolution B, which has a small gravity feel cup and a .3mm tip.  That's perfect size for painting cranks and for shooting acrylic airbrush paints that may contain pearls and flakes.  It's a no-frills work horse airbrush that has all the Iwata quality at a very reasonable price of around $80 retail.

I picked up a couple Badger patriots from an airbrush forum.  I think they were roughly ~$50

My wife uses the Iwata Revolution CR and seems happy with it.