Granite is very expensive - probably twice that cost here in NE. Limestone here is $20/T delivered as we have many local quarries, although it's not as aesthetically pleasing as granite, it's 60% cheaper. You can source broken concrete [ask for no rebar] delivered for free. As most of it will be beneath the water line, it's not a bad option, and the free part is always nice. Call any dumpster companies and tell them you have a free place to dispose of sidewalk/driveway concrete - in my experience they will be happy to receive your call.

Consider using concrete beneath the water line, and top dress the last couple feet beyond freeboard with granite. Why spend $ on granite when you'll never be able to see it? Should cut your project cost by 50-75%.

Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau

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