Covers like this are all over the place in terms of price.
My Scott Specialized Catalog (2011 edition) suggests that Scott #724 (William Penn Stamp) postmarked October 25, 1932 in Washington, DC has a catalog value of only $1.25, however, that would assume the cover was uncacheted, with the introductory section of the catalog suggesting that covers with printed cachets (before Scott #772)
"sell at a substantial premium". That premium is generally what a buyer is willing to pay and a seller is willing to accept for the item.
As a comparison, James McCusker's FDC website (which is often considered overpriced for FDC's) shows an example of virtually the identical cover with the USS Constitution postmark for $40.50 (discounted from their "regular" price of $45.00). It goes on to suggest that the cachetmaker is unknown, but the cachet is identified merely as Planty #4:

Very often these specialized cachets, often produced in limited numbers, can make the cover more valuable than either the stamp or the postmark.