What really sets CD players apart, anyway?

Aside from SACD, what makes one CD player sound better than the other? I've heard that most CD's are mastered with 24bits of data but that most CD players only sample 20 and discard the rest? So a good CD player samples all 24? And what about HDCD encoding?

I'm sure that most of it has to do with the processing chip but what should I look for?

What's the difference between a "transport" and a "player?"

Is there a really good universal disc player out there for less than $1000? ?500?