Besar or kecil?
any requirements on DC?
Living requirements? cheap as possible or proper living or high class living?

Basically kecil has more night life and more happening. Besar is more laid back and quiet.

Erm. dude.. Google perhentian kecil resorts and you shall find a whole list.
Also it depends which DC u are going to for the accommodations.

I would suggest to choose a dive center first, then see what are the available hotels nearby. No point getting a hotel faraway from the dive center.
For packages, you can refer to http://www.pinganchorage.com.my/perhentian_island.htm Don't know if he rates are updated or not.

For diving, most likely you'll pay the hotel per night. Deal with the hotel directly if possible. You have to call them up to find out. Sometimes they have off peak season rates. For 1 or 2 people, and during off peak season, some of us also just walk in and check which hotels are cheaper.