I agree with the first poster the time to question postage is before you bid and pay.

Before the OP bid they assumed that the seller has entered valid info into the calculator, and the sum showing is what the postage will cost.

If the postage was 1/2 of listed cost, the seller is making money on postage and ripping eBay off on fees = that means all the honest sellers, who only charge dollar or so for handling (or do not charge handling at all) are supporting those who do not pay their fair share.