jmc

Cubing both sides of the equation $1\text{ yd.}=3\text{ ft.}$, we find that $1{\text{ yd.}}^3=27{\text{ ft.}}^3$. Therefore, there are $27\cdot 5$ cubic feet in 5 cubic yards. Multiplying the number of cubic feet by the cost per cubic foot, we find that the total cost is $27\cdot 5\cdot 6=27\cdot 30=\boxed{810}$ dollars.