Yep, $2 for up to 20 mins in the Domestic/International short term parking lot. See:
Brisbane Airport - Car Parking - Domestic Terminal - Valet Parking, Undercover Parking, Car wash
Brisbane Airport - Airport Parking - International Terminal - Car Parking
Rises quite exponentially after the 20 mins (eg $6 for 30 mins, $10 for an hour), before settling down again after the 1st hour at $2/hour until 6 hours. Anything over that starts to be pretty expensive.
Also, Brisbane Airport just recently (or are about to) increase the taxi exit fee by 50% to $3. They make their money out of people quite easily..