+Matt
+Magnus
Cost of living is what you make it, as I'm sure you're plenty aware. Do you really need western branded groceries? Do you really need to golf at that high end country club? (of course, not literally You, yourself Mustafa, just examples lol)
Live(shop) like the locals and I think you'll be just fine on pera (tagalog for Money).
Pao says there is not much available around Manila, Batangas, PG, and he may well be correct. But I still think it's the best (obvious) first check. The area is SUPER saturated with tourism because it is easy to get to and good diving. But that also means it is quite accessible to people, like yourself, who got here first.
Already being DI/DM definitely helps. Maybe check in with Asia Divers PG (also location in Dumagete), Atlantis, Dive&Trek, or Portulano. Or you could look at slightly more "remote" destinations; Coron, El Nido, Bohol, Tubbataha, Siquijor, Caramoan.
Asia Divers has a pretty robust IDC program.... Maybe they're in need of IDC Staff Instructors??
Also, Magnus' post is how I understand the Business situation. Definitely possible, good potential for success, but also sort of a PITA with Barangay, Provincial, and Federal requirements which can take some time and/or the runaround.
Definitely let me know when you come out, at minimum let's catch a beer and chat.