Whether on Mac or not, you still have to install something with every service you use. Have to install with Join.me. Have to install with others as well - except Google Hangout, but that's not what it's for.
As far as charging, it's better to use GoToTraining - not GoToMeeting - two different things. GoToTraining has a scheduling and invite system. You can publish the invite to a web site. And, you can charge the attendee or make it free.