Create incentivesed payment option on my site.

We have site called [login to view URL] and we charge the user for watching football videos. We like to create an option whereb the user can pay by responding to an advertisement. We have the advertisement links already but need a way for it to allow the viewer to se the video once they have responded to the advert. Please can you let me know if you can help, how much you'll charge and some examples if youve created similar incentive based sites? Thanks, Algie