re: Cost range for waterfall countertop island?

I'm no pro here, but I can give you a point of reference.

I'm in the process of building an outdoor kitchen with granite countertops and a waterfall edge on one side. I need 57 sf of stone for the job. Installation is $1775 and the slab was $1111. The granite I picked, I'm told, was reasonably priced compared to other options.

This shouldn't really help you too much, though. As others have said, these projects are too variable to estimate pricing without knowing all of the information. Not only could the stone you like be much more expensive per sf, but the amount of waste could be greater depending on the veining patterns, particularly if you are doing 2 waterfall edges.