How much work is preparing a MOOC-ish course
I have a couple of strong opinions on this:


Just because many MOOCs are built around video does not make them a good idea. See this article by Lorena Barba for one example. It is hard to use recorded material well, as I've found from my own experience.
Preparing high quality videos is a job for an expert. If you don't know enough about producing the material to estimate how long it will take, the answer is too long.


I have worked on MOOC-like courses in the past and my experience is that they're considerably more time and resource intensive than standard in-person courses. I also believe that the idea that you'll save time through re-use is generally wrong, if you want good engagement with students. I think there is a lot you can learn about pedagogy, presentation and your field by working on and collaborating with a MOOC, but you've got to put in lots of time - my estimate is that setting up a MOOC style course is more than twice the effort of a standard course, and if you're recording video to a decent standard I'd raise that multiplier considerably.