I think it depends A LOT on where you are located. At the Asian markets here in Charlotte, NC, duck eggs sell for $1 EACH (yes, that's $12 a dozen). However, I would never expect to get that much just through advertising on craigslist or something--the Asian markets are selling to a demographic that is accustomed to duck eggs and also that knows they are hard to find in our chicken-egg-centric country.
I have advertised on craigslist, with no interest, for $5 a dozen. I know chicken eggs sell very well at $2 a dozen, and I have had many requests to purchase my duck eggs, but I have never come to a price I feel comfortable asking of my friends and acquaintances. So I have no idea how much I could get for them. Once my flock is re-built (I've had some casualties lately and am down to two hens, which is barely enough to keep my family supplied), I may get back to trying to sell, and I think I'm going to try them at $3 a dozen to begin with.
So, anyway, that's not really helpful, is it?

Basically, I would just pick a price, maybe based on the price of organic eggs at the grocery store, and try it for a while. If you don't get a lot of interest, lower your price. I once received the very good advice that it is easier to lower your price than it is to raise it, so start high and work your way down.
If there are Asian markets in your area, you might see if they are interested in buying your eggs. Or advertise on bulletin boards in areas that cater to Asian immigrants. Alternately, start marketing your eggs by taking devilled duck eggs to picnics and potlucks, and then sell them to your friends and acquaintances who are now hooked.
If you do it that way, you can ask them how much they expect to pay for a dozen eggs, and that will give you an idea on pricing too.
One other option that I've had excellent luck with is barter. When my flock was in better condition, I traded for home-baked bread, farm-fresh milk, and other items. I got a better "exchange rate" doing it that way (after all, a gallon of high quality milk is easily $5--much more than I can get for a dozen eggs; likewise a large loaf of high quality bread), and it was very satisfying. Another advantage of this approach is that people who are already raising some of their own food are usually more willing to try something non-mainstream, and also more appreciative of what goes into producing real food. So it's gratifying in that way too.
Anyway, good luck with it, and have fun. That's what it's all about.