The formula for the volume of a cone is
.. V = (1/3)*π*r^2*h
The radius (r) is half the diameter, so is 5 m. Fill in the numbers and do the arithmetic.
.. V = (1/3)*3.14*(5 m)^2*(6 m) = 157 m^3
The cost will be $25 for each of those cubic meters, so is
$25*157 = $3925.00.