To my understanding a website's terms of service is just like a regular contract. You agree to it by click "I agree" or simply by using the website. So hypothetically could a website scam people by including a term in the TOS such as "you will pay us $5.00 per page you visit in our domain"? Realistically people usually don't read TOS thoroughly for each website they go to.
You mean like this?
Of course, a website can charge you to access its pages; many do.
And yes, clicking on an "I agree" button can form a valid contract (just visiting the website can't). Historically, the law has adopted the position that if you sign it (including by clicking "I agree") you read it, you understood it and you agreed to it. It's hard to imaging how it could be otherwise because allowing people to get out of contracts by saying "I never read it" is problematical as well.
However, there are two things that mitigate against the type of term you suggest; one practical and one legal.
Practical: How do they get your money? They can ask for your credits card details and, if they do and you give them a court will probably come to the conclusion that you knowingly and willingly agreed to pay for the service. However, if they don't have any method of getting money from you, they would have to take you to court to do so. There are a number of practical problems with this like: who are you? where are you? Which court can they sue you in etc.
Legal: At common law, there exists the doctrine of unconscionability that describes terms that are so extremely unjust, or overwhelmingly one-sided in favour of the party who has the superior bargaining power, that they are contrary to good conscience. Such terms are legally unenforcable. Further, in many jurisdictions, consumer protection law often give additional protections up to and including not enforcing terms that are merely unfair not just unconscionable.