I am a fairly new diver and I try to go to nice places and dive a few times. A few months ago we went to Tahiti. As most suggest, that is where the plane lands and then you leave for another island. We spent 5 nights in an over water bungalow on Moorea at the Hilton. This was world class snorkeling. The unit has its own deck with lounge chairs, tables, a fresh water shower, and stairs into the lagoon. The lagoon is about 4-5 feet deep with great snorkeling. Tons of coral heads, hundreds of fish, crystal clear water, and the most amazing hues of color.
After these 5 nights we did an 11 night cruise on the Paul Gauguin visiting the Cook Islands of Aitutaki and Rarotonga as well as Huhaine, Bora Bora, Taha's and Moorea. This was also spectacular. I only did four dives throughout the trip but they were quite memorable.
We were so impressed with the region that yesterday I paid my deposit on a trip in June to Fiji with 8 nights at one island resort and a 6 night cruise on the Blue Lagoon ship (about 50 passengers).
Suprisingly Costco has some decent prices to Tahiti. The air to Tahiti and Fiji, out of LAX, are about the same. While slightly over your budget you can do a 7 night Paul Gauguin (real 5 star ship) cruise around the Society Islands for about $3400 a person which includes free air from LAX. Everything on the ship, including liquor, is included.