It varies a lot by region, of course, as well as varying by individual dive shop. Here on Guam, when everything's going well economically and there are plenty of tourists, instructors can make decent money. Most of this would be through the "intro" diver traffic (like PADI Discover Scuba.) Normally DMs can not lead intro groups unless they go through an extra short bit of training, so the numbers here refer mostly to instructors. A lot of instructors prefer to do intro diving....the reason is that they can do 1~4 dives per day, and a ballpark figure would be $100~120 for 2 dives (maybe work 7AM to 1PM) and close to $200 or even more for 4 dives (work about 7AM to 5 or 6PM). So, it's decent pay for intro diving, but it's not as interesting (limited sites, max depth 12m/40') and more stressful (a lot higher "panic" percentage) than boat diving. For boat diving, however, the going rate here is $100 for 2 dives....which would be about 7AM to 2 or 3PM. So, for the (to quote Tom Cruise, for whom I'm constantly mistaken, ha ha) "show me the money" instructors, they prefer to do beach intros all the time, because they'll generally make more money. (If they work on the boat in the morning doing "regular" boat divers, they're usually not available to do any of those PM intro dives, thereby missing out on another $100 or so.
So, busy season, a reliable, popular instructor/guide can make decent money. I've know some who've worked...oh....30 days or so in a row because they're in demand. I should have mentioned I'm mostly referring to the "on call" instructors, who work as needed for any shop that will take them. If it's a full time, ie. employed directly by only one shop, they make less per day (maybe $100 or so for a full day, no matter how many dives they do) but are usually guaranteed a salary, even during slow seasons. I know some instructors who have been offered that sort of employment, but they (if they can keep busy) might make the same amount of $ in 2 or 3 weeks, with more scheduling freedom as an "independent" than working a month as a regular employee. The big drawback is, when they tourists don't show up (post typhoon, SARS in Asia, whatever) these independent instructors aren't needed, and might not get any work.
That's sort of the basics here in working with tourists, primarily...I'm not as familiar with what people make when mostly teaching locals and/or military. Instructors probably make the best money if they can independently teach a group to dive....but that's not real regular work.