Are you hatching your eggs for them, or just hatching eggs they bring you? I have not had anyone ask me to hatch their eggs...luckily they just want me to hatch some of my breeds for them. I wouldn't know what to charge, good question!
I had three people at the feed store today ask me if I would take their eggs and hatch them out... Now that I can do 300 eggs I expected to have some ask if I would hatch MY eggs for them, but was not prepared for someone to ask to bring their eggs to me....