for 4 years I was paid $300 CAD as a DM for the usual 2 weekend PADI OW course. I figured that one course pretty much covered membership & insurance (I was only insured for assisting, not leading courses like DSD, refresher, etc.), another paid for my gas, and after that was profit. My 4 year total was $3,200 CAD and $10 US. Figured that the cost of the DM course was covered with that pay as well as the other stuff, with a few bucks left over. Hour wise, the pay probably amounted to minimum wage, but without pay think of the money I would've been out--all because I love scuba, enjoyed students (being a retired teacher), and got free air!.
My mind is blown! Said in my best Monty Python's Life of Brian voice, "you lucky, lucky bahstard!"
I used to teach at a shop chain where one of the owners and one of the managers complained about DM's getting free air WHEN ASSISTING courses. Their only benefit was discounted gear. Instructors would be paid max $50 per student (had to get certified, otherwise it was $25).