Some online test preparation services are free, while others are available through subscription only. Still others offer free trials, but you must be careful to cancel before you are charged.
A good example of a site that offers both free and paid options is Kaplan. Kaplan offers free resources, such as practice tests, but also offers online, individual tutoring. As of 2015, Kaplan's paid online test preparation classes start at $899. Using the free resources available online may provide test-takers the extra practice they need, but if they want more direct instruction and tutoring, they may have to pay a fee.