For that budget you can reach pretty high.
I'd assume you're looking for dual-action, but what else? Gravity feed, side/siphon feed?
My three current brushes all fall around your range...
Iwata Eclipse HP-CS (stocked by Hobby Lobby, so it's a steal with the 40% off coupon) - Great general airbrush. Comes with a .35 needle/nozzle but can take .5mm as well. Very well built. Mine's been acting a bit fussy lately despite deep cleaning.
Iwata Eclipse HP-C Plus - Great for fine detail work. Excellent feel. Sucks for wide coverage, though (I believe the .3mm needle is the biggest it can go), so it sucks for, say, painting big swaths of uniform colors. Awesome, awesome brush, but I wouldn't recommend it as your main weapon.
Grex Tritium TG - The trigger grip definitely makes for a more stable painting platform. Sprays fine and sprays well. Seems to clean out a bit easier than the Iwatas. The manual specifically states to not use ammonia through it, so if you use Windex to clean up after acrylics, move on.
Personally...I'm less than won over by the Grex. For small jobs, it's awesome, but if you're doing something like mottling a Luftwaffe plane, the trigger operation can get fussy, and staying at it for a long time can lead to crazy cramps in your hands.
Of the three, the HP-CS is my favorite all-arounder, but I'm still looking for my perfect brush. Currently trying to decide between a H&S Evolution and Badger Patriot.
On the Bench: 1/32 Trumpeter P-47 | 1/32 Hasegawa Bf 109G | 1/144 Eduard MiG-21MF x2
On Deck: 1/350 HMS Dreadnought
Blog/Completed Builds: doogsmodels.com