I'm not entirely sure the faculty cost will be lower longer-term, but it depends on a lot of factors that influence how the market will develop, so I can't say for sure. One reason I think it might turn out higher is that MOOCs may be taught by fewer but more super-star professors than traditional universities. Right now the difference between a top and a mediocre professor in pay is not huge, maybe 2x-3x. But if MOOCs succeed in producing really massive-scale courses, the most popular, charismatic professors could become real media superstars. And if they do, and the market is big and competitive enough to support it, they might be able to garner huge salaries through bidding wars between MOOC providers.
For example, imagine that someone like Richard Feynman, rather than giving his famous lecture series at Caltech for his regular Caltech salary, were doing it in a future era of well-developed MOOCs. He announces he's going to do one final series of physics lectures, but he hasn't decided which MOOC company he's going to do it for. I bet he could negotiate a huge fee for that, much more than even a top-end professor is currently paid. Moving back to the modern day, what if, say, Elon Musk offered to teach a MOOC? You could go for a cheaper, less well-known lecturer, but then you risk looking like the 2nd-rate MOOC company compared to your competitors.
If that's how the market develops, MOOCs might have to pay fees closer to what the public-speaking circuit currently pays prominent lecturers, if they want to attract the top speakers. And those fees are orders of magnitudes higher than what a professor currently makes.
That is why I didn't put it as dollars and cents. If Musk is teaching a class, whether to 100 or 10000 students the cost to him is his time. If he teaches for free then the students capture all the value. Or he could try to capture most of the value for himself. Think of it this way suppose there is total value (or utility) V created through teaching and the cost is C, then the value added is V-C. The value added could go to the professor or the students but either way there is a net benefit to lowering C.
For example, imagine that someone like Richard Feynman, rather than giving his famous lecture series at Caltech for his regular Caltech salary, were doing it in a future era of well-developed MOOCs. He announces he's going to do one final series of physics lectures, but he hasn't decided which MOOC company he's going to do it for. I bet he could negotiate a huge fee for that, much more than even a top-end professor is currently paid. Moving back to the modern day, what if, say, Elon Musk offered to teach a MOOC? You could go for a cheaper, less well-known lecturer, but then you risk looking like the 2nd-rate MOOC company compared to your competitors.
If that's how the market develops, MOOCs might have to pay fees closer to what the public-speaking circuit currently pays prominent lecturers, if they want to attract the top speakers. And those fees are orders of magnitudes higher than what a professor currently makes.