$5 Is completely reasonable. I've seen $6. A quick look online has prices at $8-$10 plus Shipping. People expect to pay more for Organic and you should charge it.
Best method...Determine your Feed Cost every month for the productive season. Keep track of the number of Eggs Harvested. Feed Cost ÷ Number of Dozens of Eggs +The Cost of Cartons + the Cost of Printed Labels ( If using for good Advertising) = Minimum Sell Price, Per Dozen, to Break Even. You may find you can't get the Break Even $$$$ so evaluate if it's worth it. On the other hand, if you are near an Upper Middle Class Town or City, you can make a Profit. Example...Rent a Table at the local Farmer's or Flea Market. Sit there with 6 to 12 Dozen, at the Price you need and see what happens. If you Sell Out in less than, say an hour or two, the business is feasable. Add a the largest number of Ducks your infrastructure can handle. When they start Laying, get some Poster Size pretty Pics of your Ducks and Farm Printed, Dont forget a Company Name and Logo Sign with Contact Info. Go back to the Farmer's Market and You'll be making BANK! BE CAREFUL WHAT YOU WISH FOR...JJ