The Ningaloo Reef in Western Australia is compared to the Great Barrier Reef quite small. It’s “only” 250 kilometres long. :) But I would recommend to visit it instead of the Great Barrier Reef.
Why? It’s right at the coast and at some locations it’s only 5 meters away of the beach and the furthest is about 4 km. That means that you can save a lot of money as you don’t have to pay the expensive and to about 4 hours long boat trips of the Great Barrier Reef. All you need are some fins and a snorkel.
There are two spots which I can recommend you.
One is Exmouth:
and the other is further south Coral Bay: