[RUNNERBUN]

Yes, I have also been caught in paying inflated postage cost for empty box space. Now I always ask for a firm postage and handling quote before confirming an order. Applies to retail as well as Ebay sellers. If I don't receive a firm quote (or it will be about $??) I just move on. That way I don't get any unpleasant surprises.
Obviously, if you are looking at purchasing an item of large cubic size and the item vale is low, the postage value will appear completely out of proportion in which case your only option is to grin and bear it,buy locally or go without.