Depending on how much you need I personally wouldn't pay mor than like 3.50 lb for it. I say this because I can have it delivered to my house for that so why pay more.
Cured vs uncured. hmmmm Well if you are just setting up a tank uncured is just as good as cure, maybe even better as it help get the cycle going and build a solid bacterial garden in your tank. If your tank is cycled and you are adding rock, well then I would personally rather cure it at home to besure that it is fully cured before sticking it into my tank.
All this to say that unless you are only adding a pound or two, I would buy online. If the pieces are bigger tan what you want, well that is what they make hammers for,,,