As a DM, I get paid to go assist with classes in the quarry a few hours away. Its not amazing pay, but I more view it as "breaking even on a dive day." The shop I work for pays more than the other local shops. I really enjoy assisting with the courses (they are kept small and slow) and I really like helping students with the same anxieties I initially had really get comfortable and enjoy diving. The shop pays for my entry and air, and normally feeds me lunch/dinner after wherever we decide to eat. The pay I get becomes "gas to get to and from the quarry" money, plus snacks. I try to carpool with the instructor most of the time (which means no using my pay on gas money), so sometimes I come out with a little money that goes right into my "scuba fund." I come out a little bit more ahead on pool sessions as I don't need to dump money into gas.
I of course get gear discounts, as any other DM. Another "perk" I get is if I am not scheduled to assist with a course at the quarry, but the instructor is down there with a class, I can tag along and still get my entry paid. I can then go do my own dives, or occasionally dive with some stray that wanders into the quarry without reading the "no solo diving without a solo cert" rules...The quarry will allow them to try and tag along with a shop when they go to check in with no buddy. I get a rando dive buddy for the day, and have occasionally gotten tips for that.
I have a well paying "normal" job, and I cannot see managing to pay bills as a DM in a "non-ocean" area around here. I do it for the fun, the experience, and to justify putting money into scuba gear (if I made the money doing scuba work, it goes back into scuba...or so is the justification I use with my wife). I also just dive a lot more than I would if I were not working as a DM. I can justify going to the quarry every weekend (because "I Am Working").