This really ticks me off! I don't care if you already paid or not, contact the seller stating it could of been shipped in a flat rate box for $10.95 (?), and ask for an adjustment. The price of postage will not be on the package if the seller prints a label thru Ebay. You'll see the weight, but not costs. Also let them know that you're contacting Ebay regarding the high shipping fees. If he doesn't adjust, make sure to list your complaint in your feedback and give a low rating on shipping.
If he's a top seller, he really won't care because he sells a lot of items and it probably won't affect him much.
Bottom line...Ask for an adjustment!