I just got back from Indonesia and dove in the province of Sumatra...Pulau Weh to be exact. You catch a ferry boat out of Bande Ache. The diving was very good. And the cost was dirt cheap!!!!
On the water bungalows can be had for $20 per night. Meals (breakfast, lunch. dinner) are about $10 per person per day. The diving with Ibioh Dive Center was top notch and if you purchase more than 10 dives the cost is under $20 per dive!! IDC's rental gear is top notch...I rented instead of lugging my rig to Indonesia.
The little beach town of Ibiho isn't much. There isn't a party scene at all. In fact it is about the quietest place I have ever been in my life. You can't legally buy booze but you can bring in your own.
The diving is every bit as good and possibly better than Turneffe Atoll in Belize. We saw tons of critters: Sharks, rays, cuttlefish, barracuda, etc. The reefs were healthy and there are about 25 dive site within a 10 minute boat ride of IDC.
If you like current/drift diving, Ibiho has that too in spades!!!
Fly to Kuala Lumpor and then take a 2 hour $125 flight to Bande Ache. The ferry is about $5 to Pulau Weh.
Per person costs:
Room $10-$15
Eating - $10-$15
2 dives per day - $35-$40
So for $70 per day you can have 2 great dives, eat great local food, and relax in one of the most chill places on the planet.
Hope this helps