Forum

You can moderate all content coming into the site from external sources such as site visitors or freelance writers, etc.  You also have the ability to convert a comment into a new article or topic.

Cost - free, included in all packages

Create a list of hot topic that you feel will draw in the reader that you want to subscribe to your service.  You can then right various articles that fall under these topics.  All new articles are featured on the news page but can be mined to using the forum filter.

Consider including the advertising module once you have an audience or subscriber base.