Charges? Specifically for the interview? I guess mine does too, but it's more of a small fee added to tuition to use the letter service, attend application seminars, mock interviews, etc.
That being said, more than just looking at questions online and thinking you know answers to stuff, it's important to sit in front of a stranger and get some feedback. Video feedback is good too. You might do all sorts of weird distracting stuff you don't know about. Even a dental student who you don't know since they can ask some real questions.
I would definitely recommend doing a mock interview at least once. My career center offers mock interviews throughout the year for free. They even record the interview so you can see your tendencies and even critique yourself, along with their professional feedback.