So being a bargain hunter, I have always stocked up on Catsan Clumping Clay whenever seen on special (Big W had it for $11/15kg a few months back).
This time when it came time to buy, I could not find anything on special, and so the search began.
Looking at the Catsan box, I find the litter is made of "Bentonite Clay".
Some research on Bentonite Clay results in finding that it is used in stockfeed as a binder.
A quick call to my local stockfeed joint (Gibbs), and I find they have Granulated Sodium Bentonite in 25kg bags for $18.
This is the only stock feed place I have called, and will be on the search for even cheaper sources next time I need to buy.
So end result, clumping cat litter EXACTLY the same as Catsan for half the RRP any day of the week!
Ensure you get the granulated version.
I usually buy the Aldi one. I can't recall the price/volume.