$800 for insurance may sound like a lot, but it is only for basic liability. If you, for example, deal with other aspects of the job, like gas blending, you need to purchase riders. I know instructors paying about $2,000 total for one year of insurance.
One thought I have is the lawsuit strategy that started a little over a decade ago with the drifting Dan Carlock case. In that case, a dive club chartered a boat for a 3-tank dive trip, and two members of the club, who were certified DMs, took the roll after each dive. They missed DAN, and he drifted on the surface for hours before being picked up. In the lawsuit, the plaintiff argued that the two DMs, who were acting solely as part of their club, were agents of PADI, and they successfully included PADI in the lawsuit, even though no one n PADI would have known the dive trip was going on, let alone supervised the actions of the DMs.
Well, PADI and the other agencies have now changed their liability waivers to include the understanding that DMs and instructors do not work for them, do not act under their direction, and are therefore not agents, but that does not seem to make a difference. If a DM or instructor screws up these days and a lawsuit follows, the agency that certified them is automatically included in the lawsuit. This, of course, has a tremendous impact on all costs associated with scuba.