Good day,
This is not a bid as I need some more details.
For example, what is used for? Is it for a kind of school? Because there would be some specific changes for a school to allow different department and levels or that it is used for training.
On the other hand, what type of selling do you want, Moodle provides only one price for one course per one user, if you need other than that, then I have to know details in order to decide what developments are needed.
Awaiting your reply,
Best regards,