Also check with your school's student association (SA).
I went to a UC, and the the SA already has a note-taking program for most classes. The SA in turn sells copies of the notes, or freely provide them to the hearing impared, so I was told, to raise money for other SA functions.
Clearly selling notes is both practical and profitable, since SA employed a bunch of note-takers, though at sweatshop rates.
Just to think about your competition, if you wanted to do this for money. And I emphasize think, not competition.