My fee calculator says 4.95% total for eBay and PayPal fees combined. Pretty sure that PayPal would choke on a single transaction that size, though, and I'd like to think Mike would be in a position to get more favorable terms anyhow...
For that kind of money, chances are a deposit would be done through paypal, and the coins would be hand delivered. If it were me, I wouldn't want to trust Paypal, or the PO.
As mentioned, the total eBay/PayPal fees are less than 5%. That is a relative bargain compared with the major auction houses which currently charge buyer's premiums ranging from 10%-17.5% and some charge seller's premiums on top of that!! Plus with an auction house, you have to wait anywhere from a few weeks to several months for your coins to get listed, sold and then for you to get paid. People regularly complain about the high fees of doing business on eBay, but if you're willing to do a little of the work yourself, there is nowhere else to reach so many potential buyers for such a small fee.