No, things cost what buyers are willing to pay. Transparency would be saying the product costs the total sum so that everyone making purchasing decison knows the total cost. A manual in this case is as much part of the plane as is the wing! The product is a pile of metal without the docs. Is there a separate cost like this for R&D,labor,parts,paint, "service charge"? I mean come on,imagine the outrage here if microsoft made msdn cost even $10/year!
Salaried employees don't get paid by hour our output. If it takes a team a half a year to write the doc, they still get paid for the rest of the year.
Regardless, the cost nevet reflects the effort put into it. It is simply what they charge because they can and because the buyer pays and because the competition is not offering something better when bidding.