You can audit the classes for free, which lets you watch the videos, and take the quizzes but not submit them (which is annoying).

How about this 7-day "trial"? all those courses seem pretty short (estimated 5 courses x 3 weeks x 4 hours = 60 hours), so if you do them full time and manage to finish within that 7-day trial would you receive certificate for free?

This one appears to be (but it's also not available for enrollment just yet). Then, for example, his ML course (https://www.coursera.org/learn/machine-learning) is available for purchase: http://collabshot.com/show/1hWhMQ