Disable free visitor registration

Hi guys. Am I using the right plugin? Here's what I'm trying to do.

I have a directory and the only pages that I want closed for visitors are the event and listing submission pages and a member area page. The rest of the website is viewable to all without having to login.

The only subscribers I want are premium ones. No free subscription.

How do I prevent free subscribers (default WP) from subscribing?

Thank you