Damon,
We are in the same stage and the fill level on our block is similar to yours - around 900mm to 1300mm. Our builder will design the slab for a P classified site, but it won't be waffle pod slab because that is not good enough for our site. Hence, we will have a "conventional" slab (raft slab plus piers & beams I think).
Re the cost of your slab - I guess it all depends on what type. Like Samira said waffle pod slab is cheaper.