I can deliver this to you in one day.
I am a senior developer for a web development firm based in USA.
I work as the senior wordpress developer at this firm.
I will build you a gated content system where you can protect pages to only logged in members of your site.
The solution will also include a shortcode for a login form that will force your users to log in to view the content.
You will be able to set this on a page by page, post by post, basis.
There will also be a shortcode included to allow you to protect specific content on the page.