Enable Populi to add up the total dollar value of library collections and materials

One of the things I have to report to my superiors is the total dollar value of the books (and CDs, DVDs and other library materials) in the library. The library function in Populi provides a place for recording the dollar value of each book and for other library resources; but as far as I can tell, it does not enable us to determine the total dollar value of our whole library collection. It seems that it should not be too difficult to set up the system to provide the total value, and it would be very useful to us if we could do this.