We've had success: We have a sliding scale: zero for groups with no money, $25/hr for small groups with small budgets, $45/hr for workshop at a school or community location, $65/hr for a large non-profit or business.

We include one staff, 1-3 volunteers, tools and supplies. Examples of 'workshops': we are the 'fixit' station at a school bike rodeo, we help fix bikes at an apartment building, provide oil and air at a University event, etc

Actual hands on bike fixing help seems to be much more in demand than a more general maintenance class, yet those work too for donations, $5 a class or set fee for series of classes.