All of the reasonably priced dedicated Camber Bars we have seen may work well for the "camber" part, meaning the dropped weights, but tend to be pretty crappy bars, the part between the collars.  Smooth, inconsistent knurling, or too small or too big diameter.  

With this attachment, you can turn your own favourite squatting bar into a camber bar, and for a fraction of the price.  A Rogue camber bar is $385 C (and has NO knurling at all) and their Pro Loc Camber attachment is $176 including collars that you might not need.  

What does a Camber bar do? By lowering the weight, it changes the centre of gravity, moving it forward, putting more emphasis on your hamstrings and lower back.  Think of it as doing both a squat and a "Good Morning" at the same time.  

Another great use for this attachment is for overhead presses when you have low ceilings, like in a basement gym.  

Ours are not the only such product out there, but at $129.95 a pair shipped, they are the lowest price!