What courses are free and what aren’t free? I am sorry but new to this site !
All of the code.org curriculum is free to use. You can create a teacher account and then classrooms and your students can enroll in your classroom and there is no charge for any of the courses.
If you aren’t sure where to start, let us know what grades / ages you teach and we can point you in the right direction.
The curriculum for CS Discoveries and CS Principles (the two full year courses) can be found at http://curriculum.code.org. There are also links to Hour of Code activities and a course that can be used in teaching Algebra.
Let us know if we can help you in any other way.