Online video resource for customers

Hi there,

I am not quite sure how to pitch this question.
We are a small company who organise and run medical training courses.
We are now looking in to filming the lectures that take place at our events and put them online for paying customers (saves travelling miles to see them in a venue when you could quite easily see them from home.

In a few months we should have collected and edited enough content to begin the project.

I have created a new website for our company on WordPress and I would like to use it for the site that will be the host of the videos.

What I will need is a plugin that will allow control over purchased content.
I want a customer to be able to register on the site and then have the option to purchase a package of videos.

For example a Radiologist will sign up and pay ￡100 – this transaction will then allow them to access 6 online one hour video lectures.

Is there a module/plugin that can accommodate this? We are happy to pay for the right software.

Ultimately the site would be able to offer certificates for each batch of viewed lectures.

I would appreciate any input for this project.

Many thanks,
Jack