Pro sites / pay to blog

Hi,

I need to create a site, where about 400 courses are sold separately. Trying to figure out how to do it. My idea was, that each "course" would be a separate site under multisite network. So users only log in once to the multisite and then they could buy rights to use spesific sites on the network (with their existing usernames). Is this a working approach or do you suggest something else?