We did it last year! I think there were six or seven families in total, we drove to Sydney and camped there for a week rather than book a hotel. We stayed at Lane Cove River Tourist Park, if you didn't want to camp you could consider booking a cabin there maybe? Not sure how much they were but our powered site cost us $260 for the week! For NYE we booked Bradley's Head which is the next headland to Taronga Zoo. It was split into two areas, one was for families and we all took chairs, rugs and picnics. This area didn't allow alcohol though. The other area which was inside a kind of clubhouse had a full bar and a band playing. Again, not sure how much that option would be but our area was about $35 each and tickets were limited so that it wasn't too crowded. Thoroughly recommend you do it, it was definitely one off my bucket list!