Facebook will never charge you money for having a Facebook account or for using a normal Facebook account.
Commercial accounts are charged fee’s but that is because they are commercial in nature and either promoting good and or services. Facebook users will not be charged anything, and for one simple reason, YOU are the product!
Facebook makes it’s money from selling your information to Advertisers and Marketing research companies, as well as various other organizations, both Government and private.
If they did impose a fee for using Facebook they risk losing millions of users, this would decrease their marketable base and therefor impact on their bottom line.
Remember, If it is free, then you are most likely the product.