I wouldn't necessarily pay for an online course, partly because I'm "cheap" and more reluctant to pay for a lot of things than most people, and partly because my life is going rather smoothly right now and I'm not sure how much added benefit I could get out of a $75 course. That being said, I pay significantly more than $75 to learn martial arts, for the main reason that it's fun and thus makes my life better. So if I had good evidence that your rationality course was fun, that might sway me. And when I translate $75 into my current hourly wage, it does seem that the good (and fun) obtained from such a course is worth as much as a shortish day at work.

Anyway best of luck!