I would love to be more help, but I'm afraid the answer I have is going to be deeply unsatisfying:
A fair price is whatever someone else is willing to pay.
Sorry.
In my case, I can't unload a *pair* of Holderread magpies for $15. Pathetic. But it's because there is simply not a demand for that breed in my area, no matter how high the quality is.
Sadly, I also can't find homes for GORGEOUS Holderread blue Runner drakes at $15, even though there's an enormous demand for Runners here. But this time of year, everyone already has their breeding stock and unless they've lost a drake, they don't want to add another, even if it is really nice quality.
I *can,* slowly, find homes for them at $5 a piece, which is pathetic because that's less than the duckling price and these babies are three months old.
But the point is, that if you have a market that *wants* what you have then you can get a much fairer price for it. Holderread can charge those high prices because everyone in the world knows his birds are the best, and furthermore anyone in the world can access them if they have the moolah to fork over, so his market's much broader than most home farms. I'm not willing to ship, and even if I did, I couldn't get the same price Holderread does because who would buy my flock rejects (even though they came from Holderread) if they could buy directly from Holderread for the same price?
So, anyway, I'm sorry I can't just give you a price. One thing you might do is check the places where you plan to advertise (craigslist, local feed stores, etc.) and see what others are charging for ducks. You can probably ask a little more because yours are Runners which are in demand in most areas nowadays (they're the "in" thing right now in a lot of places) and the supply hasn't caught up yet; plus yours are a very nice quality. Start a little higher than you think is necessary, and gradually lower your price until you find a sweet spot where they sell at the rate you want to sell them.
Good luck--and they ARE beautiful!