DR sucks, it's a great place to go with friends, get drunk, meet some hoochie and wake up in a bathtub of ice missing a kidney, but not a good place to dive.
On this side of the planet you have only two options:
1. Cozumel
2. Playa del Carmen
Both are in Mexico so call your travel agent and change your plans. Cozumel is really cheap it's an island (reef with land in the middle really) just off the coast of Cancun. It's the best diving on the east coast of the western hemisphere. The entire island is a coral reef, it doesn't matter where you stay the diving is great. I'm not kidding when I say it's a coral island, there's no beach. There are pits of sand where you can enter the reef but you have to lay down in them and pull yourself out on your stomach. There is a small shelf around the resorts but it gets deep quick and when you turn around you'll see the cliff face covered with animals. No place like it,
I stayed at the Fiesta Dive Resort which I highly recommend. If you stay there get one of the jungle huts. You have a view of the rain forest and you're right next to the "beach." If you leave your fruit basket in front of your door each morning you get a large iguana as a door man.