I am a Amazon Prime member for the exact reason of shipping charges.
After living overseas and having the high cost of shipping, I found that the Prime membership is really a cost saver. I buy a lot from Amazon because I like their return policy as well as the customer service. I know the cost up front can be a problem, but I find I save so much more over the year that it is, in the long run, a bargain.
As for the vendor that changed their ship price AFTER the fact. I would have canceled and reported to PAYPAL the problem. I only shop from vendor listed here on the board that have a proven track record. Money is too tight to be wasted!