Prices for hatching eggs?
As with anything retail, sell them for what the market is.
i.e. You are going to sell them on Craigslist: other people on CL are selling them for $25 but there's more than a few ads for $20 each, and one newer ad for $15 each. Keep an eye on the $15 ad and if it disappears, that was too cheap.
If you list them for too little, your phone will blow up and you'll have nothing to sell. Too expensive, well, they'll become breakfast. There is a happy medium, you just have to find your market. If you have "sales points" that add perceived value, that always helps. I've noticed that on any of my ads, a well written, clearly explained product, with lots of GOOD pictures will outsell anything comparable that's even cheaper. I can get 30-40% more for my products because people know what they are getting and not taking a chance on an unknown
Please resist the urge to sell them cheaper than everyone else, you'll only drag the market down and harm your own sales in the long run.
Make sure you check the full market (ebay, BYC, whatever), because if people can buy them 50% cheaper after shipping, you'll lose out there also.
I probably gave you way more information than needed Just do your due diligence and it will be a fun ride!