It really depends on the breeder and the demand, if you check ebay you can see what people are paying for them. The general rule of thumb is whatever you would sell a duckling for, sell an egg for half that price. So if you sell ducklings for $20 each. The eggs would be $10 each.
If you're talking about shipped eggs, I probably wouldn't do it. I have 12 shipped eggs in the bator at the moment and it looks like I'm not gonna get a single duckling. A total waste of $103.50. Apparently, waterfowl eggs don't ship well. BTW..I paid $9 per egg plus shipping (she did throw in 2 extras at no charge).
i just rec'd 10 call eggs from e-bay. Penn to Tenn. 2 eggs cracked and 3 had free floating air bubbles you can see when candling, they are reall watery inside, i'm thinking scrambled, but today i put in the bator anyway to see if I get lucky.
I have rec'd 5 other shipment of eggs 2 other duck and 3 chicken they were all fine. Hatch didn't go so well. most made it to 90% development and something happend in the last few days that most didn't make it. nothing wrong with the eggs, its the temp, humity, ??? sad i'd much rather had infertile eggs than a still born.