With that budget, my first choice by a mile would be DD m3 or m3a.
IF you can find one, a Cactus pf600 would be a monster, but the m3a is a better daily. Cactus would own it in the lanes though. I know where one is for that price.
Honorable mention to the Crescendo BC3500 because you cna almost get one brand new for that much with a warranty and 'nendo's customer service.
Sundown 3k... meh.
Runner up is the SoundStream DTR3400. Incredible deal for a very nice amp. Crunch GP Pro 3k is also legit.
Or you can buy my MMATS 3500 for less than your budget.
[Edit: I think you can sometimes find an AQ3500 for that budget too. Great buy.]