Some of the time you have to invest is due to the fact that this is the first time you give such a course, correct? You expect it to get more time efficiënt later on?
If so, I would base the rate you ask on amount of time you think it would cost you down the road, and not include the one-off time investment in your rate. If you want to do this in FIRE, the opportunity costs are not that relevant, I would say. You do this now not for the money (because then your regular job would be more efficient), but to try out for the long term, build contacts etc.