Password Protected Pages based on IP Address or the like

I am looking at the possibility of hosting a virtual convention on my website. We have the technology to livestream, webcast and hangout with other convention personnel, but we are still struggling with the hurdle of how to keep it off limits from those that have not paid an entry fee.

I know you can natively password protect certain pages in WordPress, but with ONE password that unlocks the page, that makes it extremely easy for anyone to just send that password off to his friends and instead of hundreds paying for admission, we get one person paying, but a few thousand attending.

What I am looking for is some sort of password enabling for pages that is user dependant, or IP dependant. Where everyone MUST have a username and password to enter the live event and the login credentials are non-transferrable.

Does anyone know of any free or premium plugin that would allow for that? If it means I have to spend a little money for this functionality, I feel it would pay for itself in the long run.

Thanks in advance.