Web consultant and founder of Saint Valley Web Consulting. Helped over 80 businesses and organisations improve their internet presence
Depending on the level of skill of the group members, I would try some affiliate offers from Clickbank. I have done some Facebook advertising of affiliate offers and I have found that photography courses and foreign language courses convert pretty well. In your position, where you have authority already as group admin, you should be able to convert a much higher percentage than I would using adverts. Look for a good course that has "rebilling" for recurring monthly compensation