Unfortunately the supply of mentors is basically nonexistent while the demand is endless. Multiple sites have tried with little success. I know one that survived by charging for it and paying their mentors but it's still way below their regularly hourly rate while it quickly becomes expensive for the student.
A potential avenue would be for self-learners to act as mentor to other self-learners. With a reputation system à la stackoverflow, mentoring tasks could be made appealing.
