If II is charging the same as the cruise line, they are probably high. A so-called ''cruise exchange'' is usually a ripoff with any exchange company, but sometimes I have seen RCI competitive with cruise discounters on their all-cash price.
You should compare not with cruise company websites but with cruise discounter websites. A good list of cruise links is on the Links Directory (on the dropdown under ''Website Navigation'') at
www.timeshareforums.com