So much depends on the market in your area. And finding customers who esteem duck eggs. Those who do may be willing to pay more than they would for chicken eggs. But many many more people think duck eggs are inedible, or at the least just as good as chicken eggs. If you're fortunate you can find some gourmet chefs & bakers, some individuals who prefer duck eggs, individuals with allergies to chicken eggs, and folks with ethnic preferences for duck eggs. Many commercial bakers cannot justify the higher price for duck eggs, they need to keep their expenses as low as possible and their customers aren't willing to pay extra just because the goods were baked with duck eggs.
Here in Palm Beach County, Florida, I can sell chicken eggs for $4 a dozen and duck eggs for $6 a dozen, delivered. But my duck customers are dwindling, I have sold them for $4-$5 when I can. And I give away a LOT of them to try & convince more folks to try them. We also EAT a lot of duck eggs, when I have a lot I make big quiches that use 12 duck eggs, or several loaves of French Toast using 30 duck eggs, 4 bananas, and a couple of loaves of challah bread.