If you're giving the class just to figure out how your courseware works, or to dip your toes in the water --- I do both somewhat regularly (as in, a few times in the last 5 years), just do free. $30 isn't even enough to work well as earnest money.
If it is targeted at intermediate level, I would certainly be glad to take it.
I'm not seeking to learn RoR, but your rate strikes me as extremely reasonable. tptacek suggests that it's too low; I'll just say that if I wanted to invest 2 hours in this, I'd certainly also be willing to invest $30.
I'd be really interested in hearing how this goes for you!
I suggest you think of things this way - can you find 3-5 (there are three below, so good marketing) people who would want to take a tutored course of say two weeks. Then you need to find a community college or similar where you can rent a room and Ethernet. The small group learning is always a better bet.
This is a pretty good idea though.