I checked out the booking rates at the Sea World Resort and Water Park (based on a superior room with 2 x double beds) for the period Friday 20/09/13 to Tuesday 24/09/13, which came to $958. That's just $191.60 per night which looks like a cheap rate compared to any other per-night-prices which I could see in their booking system for various dates throughout the rest of the year. Rates on average appear to range between $219 to $350.
To have breakfast included during your stay it'll cost an extra $22 per adult per night while each kid between the ages of 3-13yrs will only cost an extra $1 per day.
Payment required in full by credit card at time of booking. No refunds. American Express and Diners Club cards service fees are 3% while Visa and Mastercard transactions will be charged a 1.75% service fee.