I certainly dont understand the shipping calculations either.
I recently needed a sealed ball bearing for my bandsaw guides. Checked out the mfgr's website, 9.90 for the bearing. All good no biggie until i got to the shipping cost, 17.85 withing the U.S. !
they seemed to thing the little bearing which weighed about 1. 3 ounces or something like that had to be shipped via UPS.
Drop that little bugger in a padded envelope and hit the post office .
I was able to get one at my local ACE hardware for about 11.00 and I had it the same day.