This sounds to me like simple access restriction that could be accomplished by using php/mysql to store user information, authenticate users and restrict access to the content based on how many points/credits they have left.
let the users log in, then when the user accesses the page query their account to see if they have any points left, if so then display the content and update their account to deduct points. One thing to think about with this though is some way to keep it from charging them multiple times for the same page.. They might get mad if they do something like refresh the page a couple times and get charged repeatedly :D
If on the other hand you also need a CMS to manage your content, it could get a little more difficult. I don't know of any that handle something like this.. You might end up writing a plugin or modifying the code by hand.