I won't sell duck eggs for less than $4 a dozen--and that's for regular customers. My listed price is $5 a dozen, and they sell well at that price. The key is to finding the right market--people who know duck eggs and like to cook, are willing to pay more for them. And they are worth it--free range, humanely raised, no chemicals, etc.--plus ducks are more intensive than chickens--they need bathing water, they're messier, etc. So I feel quite justified selling them for that much. During times when they aren't selling well, I give them to friends and clients as gifts, or go on a baking spree or freeze them for winter.
Of course, your price depends on your market, too. I live in an urban area with a cooking college ten minutes drive away... so it's a different market from many people. Still, the key is always in finding the market that already wants what you have, or (if that market doesn't exist), creating it by showing them how your product is superior.
I see chicken eggs on craigslist for $1 a dozen all the time, and that's partly why I won't even bother with chicken eggs. That, and the fact that I like duck eggs better.