The average member in the average gym won't give two flying figs about grip strength unless you first teach them why it can benefit them. Even MMA fighters will likely need convincing that grip strength should be a priority because it generally doesn't get much attention.
Giving a free 30-minute seminar, to gauge interest and get the word out, would be a better first step instead of just popping the class up out of nowhere.
Explain three benefits that Average Joe, or Average Jane, would actually care about.
Explain three benefits specific to MMA that a competitor would care about.