You can sell your back catalog. people like Marc Maron and Adam Carolla are doing this. You can use a tools like Magic members which no only allows you to sell individuals posts, but you can create different membership levels with different features. It goes for$97 and has lots of great features.
A less expensive alternative is a wordpress Plugin call Estore which allows you to sell single files. The file location is never disclosed to the end-user (its scrambled) and you can set a time when the download link expires. This helps stop people from sharing the download link.You can pick up this plugin for $49.
If you are thinking that people will not pay for something that they use to get for free, ask anyone who has a Netflix account if they watch any TV shows (something that use to get for free). I know I do. The ability to watch/listen on demand is something people will pay for if they enjoy your content.