The Limit Posts extension enables you to limit the number of posts that may be submitted by any user role(s). So you can limit registered subscribers to, say, 3 submitted posts, and limit authors to, say, 5 submitted posts. Plugin provides a settings page where you can customize your post limits as desired. Requires USP Pro.
Check out the Limit Posts homepage to learn more.
One-time fee. Non-recurring. Free updates for the life of the plugin.