i was just in moalboal this weekend and really enjoyed it. we saw quite a few turtles, some frog fish and our first white tip since we've been in the phils. (it was just a baby). if you're on a budget it's cheaper than dumaguete/dauin and alona beach.
to get to apo island from dumaguete you have a couple of options... you can take a bus/taxi/trike to malapatay and then catch a banca over to apo... or you could stay in dumaguete or dauin and dive with one of the resorts in the area... most of them head to apo every second day or so. and that way you'd also get to dive the sights around dauin as well. Don't miss the pier it's a great spot.
as for the $$ situation, we've been here for 3 months and just hit the ATM whenever we can. there are lots of places without ATMs but since you're traveling around quite a bit it shouldn't be a problem. just hit one when you're in a major city (manial, cebu, dumaguete etc). we pay for our hotel and diving with credit cards and then use cash for everything else. most resorts will just give you a bill at the end of your stay there, including the room, and food/drinks you consume in their restaurant.
as people have said a lot of ATMs have a limit of 5,000 or 10,000 pesos... but thats usually per transaction (probably just so they can gouge more money out of you!) you can do more than one transaction in a row with no problem.
as for saftey, we have heard of a few people having money go missing from their rooms, so always use the safe in the room.
trigger fish here are MUST tamer than in thailand. i haven't had any issues with them being aggressive here at all. but i do have some teeth marks on my fins from thailand. not sure what they are like in PG... but in dauin they are fine.
enjoy your trip!