Setting up a subscription-based service

I am creating a subscription-based theme site where users pay $20 for every year they want to download the premium templates they want on the site. The problem with everything is that every ecommerce plugin that’s out there just is for buying things. That would be helpful if I was selling individual themes, but I just don’t know. Is there anyway to create this subscription-based service where users can subscribe, then have the links show up or something?

Thanks,
SuperMario290