You have pretty well answered your own question.
Tutors are independent contractors who can charge whatever they feel their services are worth or whatever they feel the traffic will bear. Anyone can put their services as a tutor on the market - this does not mean that every tutor is as good as everyone else. There are many items to be taken into consideration when looking for a good tutor.
1. Travel distance - while they may not be tutoring you or your family member while travelling, they are also unable to tutor anyone else. This time must be taken into account.
2. Their experience - you want someone who has a good and thorough knowledge of their subject; and, has taught before.
3. Their qualifications - you want a tutor with qualifications. This proves that they have reached a certain level of proficiency in their chosen subject.
4. Ability to communicate - the tutor must now be able to impart their knowledge to the student. All the qualifications and experience in the world are no good to the student if the tutor is unable to explain the subject in terms the student understands.
5. Temperment - the tutor should be even-tempered. Rages and insults do nothing to benefit the student. The tutor must be able to deal with a student who is difficult in a calm, reasoning manner. If not, again the student benefits nothing.
6. Dependable - the tutor should be there regularly and on time.
Obviously, the more positives a tutor has, the more (s)he will charge.