Steve . . .
Not ridiculous at all when one considers how critical an established relationship is between the dealer and the breeder when attempting to strike a deal.
Depending on the given breeder, and the given fish, a do-it-yourself buyer or a discount-dealer wouldn't even be invited to the 'secret greenhouse,' much less be tendered an offer to purchase the top koi Japan has to offer.
Now if all you're looking for is tatesorta, tateshita and chuppa, no need to even go to Japan -- just wait for it to show up at your local dealers. But if you do, I can guarantee you he'll be getting a lot more than a measly 20% markup.