Paid content is ideal for AVS sites especially, since you are only showing 3 or 4 teasers on the outside and selling the membership to see the content inside.
Another advantage of paid content for free sites is that you aren't tied to one sponsor, so if one company isn't converting for you it's easy to just switch out the ads and promote another outfit. No need to take down your sites or get new content. If you happen to be getting good SE traffic on a freesite that isn't selling, or one that the sponsor has dicked you around on, it's nice to own the content.
As far as price, yeah, if it's cheap it's everywhere. But if you buy some micro-niched stuff and put it on an AVS, the surfer who needs it to get off has to buy from you
So it's worth paying more for.