In the last year podcasting media hosts have been providing tools for podcasters to sell their back catalog, or premium content. Blubrry recently launched, (um and then unlaunched – it appears to have gone back to the drawing board), Cuetoo.com which allows you to sell your content on a monthly basis. I just found out about MYLibsyn from libsyn.com with both of these solutions have you splitting some of the profits with the companies. The bonus of these is these companies help with the setup. The grandfather of all premium content is premiumcast.com which charges $99 a month for their service)
Let me say up front, I love both of these companies and I've been using Libsyn since 2005. With that said, you don't need these companies to sell digital content. There are great membership plugins that make it easy to sell premium content. I just started working with Magic Members and I'm loving the interface, and the flexibility. You can sell a membership, or make a single post for sale. Very cool. Best part? it's only a ONE time fee of $97 for a single site license.
Each member gets their own RSS feed. If they end their membership, their RSS feed no longer gets new content. While this does not provide the App support that mylibsyn does, if you're looking for a way to sell premium content, or make your back catalog “premium” you can do it with the Magic Members plugin. Once things get going, you can start your own affiliate program with their magic affiliates plugin.
If you're looking for the “no hands” on approach, then things like Mylibsyn, or Cuetoo (when it comes back) may be the way to go. For the record, magic members you simply upload the plugin, active, configure some settings (lots of video support, and their teach support is very attentive if you need help), and you're good to go.