All(?) the classes are free (gratis) and are online.
The ones I've seen so far are only video lectures with some quizzes, and other supportive things like forums.
You have the option of paying in order to apply for a certification of completion.
I'm having a blast with the 2 classes I'm focusing on right now:
https://www.coursera.org/course/emergenceoflife
(memorable that lecture by a theoretical physicist - reminds me of The Big Bang Theory - and did a very good job)
https://www.coursera.org/course/thinkagainEmergence of Life
How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life!
And there's so many more broadly interesting courses like:Think Again: How to Reason and Argue
Reasoning is important. This course will teach you how to do it well. You will learn how to understand and assess arguments by other people and how to construct good arguments of your own about whatever matters to you.
Learning how to learn
The brain and space
Visual Perception and the Brain
Or even technical courses like:
Cryptography