depending on where you live, it would amount to the same sum (if not more) if your purchased paperbacks+shipping costs.
amazon apparently includes around $2/$3 as "whispernet fee". it also depends on whether the equivalent paper book is a hardback or a paperback.
then there is the public enemy no 1: the publishing house (it's the one that sets the starting price and imposes all sorts of restrictions on the sellers, like amazon)
this has been discussed over and over
if you go over to the "kindle community" at amazon, you'll see 100+ threads on the subject as well as boycotting efforts.
i still prefer the extra tariff for the advantage of having the book in under 30 seconds.