This would require a server-side solution if you wanted it automated. You would program a script in PHP to accept the money, (through a gateway or PayPal, etc.), issue a custom/unique username & password, perhaps log the ip. That user would then have access to the video for a period of time, say 24hrs.
You can code that yourself if you're good with PHP/MySQL and are hosted on a Unix or Linux server, otherwise, if you do the "pretty" work (page design) and all I have to do is the server-side code and page framework, I'd charge $200 through my development company (compusolver.com). Add $50 if I have to do design also.
Something like this would work OK through PayPal, but even better through a "real" gateway & merchant account. I am a dealer for gateway and merchant accounts & I do PayPal coding also - but then, its not that hard to do and you could probably do it yourself.
If you need hosting, I do that too:
http://www.SmBizHosting.com
I'd recommend that you be sure of your market before you invest much money. It might be best to start off offering DVDs and sell through eBay. That way you don't invest anything until you see what the market is like.