Multiple sites or can I accomplish within one site?

We are creating training class content that can be launched from WP. Each class has freely available posts/resources. Each class also has premium e-learning content. We are looking to use Membership to control access/subscriptions to specific premium content. The e-learning content can be run from a post. If I have 4 different e-learning courses, how can I use Membership to control access to each course? We want someone to pay for each premium course. That sounds like I would have to create 4 different access levels with access to 4 different launch pages for the premium content. If I bundle all this content in the same site and we have 20 courses down the road then I have to create 20 different access levels. Also, if someone purchased multiple premium courses can they be granted another access level in the same site? It sounds like this model should not be used all within the same site, but each course should have its own site so that Membership is used as a simple mechanism with a free access level and a paid access level. What do we think?