Tutor's fee can vary a lot.
(paying Uni student $40 per hour, paying a retired high school teacher $80 per hour - all cash in hand, year 12 level)
Recommendations are mostly word of mouth.
(ie. friend's child did well in HSC, so when we need to, we ask them which tutor did they went to)
A good tutor need to be up-to-date on the syllabus, and have access to past papers from various popular schools. These you can get from being a high school teacher.