Revenue from online courses?

I've been thinking more about online courses (Since I enrolled in CS253), and different possible models for revenue.

Free seems interesting and obviously useful, but maybe not right away? Here is what I was thinking:

• Course begins; $5 per class (Mostly for bandwith/server costs)
• All the lectures, reading etc is passive, and doesn't cost the teachers anything
• For every question you ask the teacher/TA, a $0.50 charge goes to your account, which you pay off monthly
• Obviously, help obtained from community support (class forums, chat) is free

This seems like it could be sustainable, especially as some of these courses get larger.

What could be done is, at the end of the course, the content is freely-accessible. Still, questions can be asked anytime for that $0.50 charge.