If you put the key in cardboard to protect it, you should put 20 cents extra for postage on the envelope and hopefully the USPS won't run it thru their machines and damage it. PayPal is gonna cost 30 cents + and PayPal charges do apply to the shipping cost.

Some people can be outrageous on their shipping charges - I believe I saw another one that wanted 4.95 for shipping 1 key. I avoid those auctions.