You would want to take into account success/failure as the outcome of such a venture. If you charge, the "customer" may have an expectation of ending up with a certain number of chicks and end up disappointed when that doesn't happen. I think I would charge a flat rate (for your time and electricity costs in running the 'bator), plus a fee per live chick. If it is set up that way prior to the hatch, she understands that she may or may not end up with any live chicks. Her eggs may not be as fertile as she would like, or may get too chilled to develop prior to her collecting them (or a whole slew of other possibilities outside of your control). I don't know what to suggest for the incubation charge but for the live chick charge, I would keep it pretty low - maybe 25c per chick. That is far cheaper than if she goes to her feed store in Spring and buys chicks but she will be happier knowing she is not paying for the eggs that were duds, while your costs are covered even if nothing hatches. Win-win.