Last year, 7 of my friends and I spent two weeks in Shoal Bay, and we all seemed to survive on $250 each for the whole two weeks; that is including decent food (tip: buy at Bi-Lo, you get petrol dockets for $30!), eating out occasionally, alcohol and entertainment, such as bowling and bingo (bingo is awesome).
It was very memorable; we went down to the beach almost every day (twas only a short walk), a couple of us brought our bikes, so we went riding some days and the best part is, there was no police, 'coz they were all up in Queensland.
The tip is to go somewhere where either you or someone you're going with knows their way around the place, and go with people you know and trust. Ask what type of place your friends would like to go to (eg. the beach, their family holiday house - which is a good idea; you don't need to pay rent).
Hope you work out where you wanna go. Have fun!