That is a BS charge. I've ordered a dozen guitars off of EBAY and none have had an issue like that. Overnight shipping should be no more than $140, so I would tell him you will pay, but that it must be over-nighted. Regular shipping should be no more than $100. He is just trying to extort you a bit and the only way that would have happened is if he would have gone to the shipping depot and basically gone through every step except for shipping to find out that charge. Maybe meet him halfway and call it a day...probably best for both of you.
Oh, and post pics.
"I believe that banking institutions are more dangerous to our liberties than standing armies. If the American people ever allow private banks to control the issue of their currency, first by inflation, then by deflation, the banks and corporations that will grow up around the banks will deprive the people of all property until their children wake-up homeless on the continent their fathers conquered."
-Thomas Jefferson 1802