Indeed it depends on where and how you work as a CFI.

When I was growing up through the ratings, the CFI I had for solo owned his airplanes and charged about $50/hr for a 10-hour block of time (C-150 rates back in the day, well, not that far back. His C172 was $75/hr for a 10-hour block I believe, but it broke so I settled with the C150).

After soloing in California during the summer, I continued my PVT at Benson, AZ where the FBO owned the aircraft and I paid my CFI and the aircraft seperately. I believe my CFI had to give $5/hr to the FBO for insurance, the rest he kept. I believe he charged me a total of $25/hr (he was an older gentleman who truly enjoyed fliying and wasn't looking to time build or make flying his sole source of revenue, he owned a gas station at the time.)

Then I continued my ratings at ERAU-PRC, where I now am CFI-ing. I am paid $16.08/hr of contact time plus $100 per two-week pay period to count for the time I spend working while not in contact with a student. $16.08 is starting pay for a CFI with less than 750hr dual given and at least a Bachelor's degree. Students currently pay the school $51/hr for me. However, if I gain at least 50 hours of contact time in a pay period, I get a 15% raise. For at least 60 hours of contact time in a pay period, I'll get a 25% raise. So, as long as I have students and can get them on the schedule, it works out to be not that bad of pay, especially whilest living with two other roommates. When I got my W-2's, considering the total amount of contact time for what I grossed, it came out to $20-21/hr before taxes.