Base rock & Live rock
 

What's the difference between fiji base rock and fiji live rock? Is it uncured rock?

It's all live, but the base is usually the real ugly stuff from the bottom of the barrel. Little or no corraline, no other organisms, etc.

do ppl usually use these? or all premium fiji live rock is best?

another thing, are uncured rock and cured rock sold off at the same price? or are uncured rocks cheaper?

Base is fine to build your pile on. Biologivally it does the same thing, filtration wise, as any other rock. So don't feel it's inferior.
Cured rock is generally more money just because somebody had to cure it using their time and salt water.