Iain,
My son Gavos999 off the forum and his son Benjamin (6) went for the day when they were over a few weeks ago, they had a great day and really enjoyed it.
Its costs 25YTL for an adult and 15YTL for children 5-14 years, Calis Beach Restaurant on the front do still as far as I know give fre tickets of you eat a main meal there, and yes he is the brother of the Aqua Park owner, I am sure that if you have bought 2 drinks you get one or some free as well in there.
If you walk along the prom from where you are until you reach the new seating area and ER OZ is infront of you, turn left, go over the bridge and up the road turn right at the traffic lights and its just up on the right after the 'Orient'Hotel....you cant miss it.....