I generally go to Chemist Warehouse for my scripts, but to be honest I've never really done a proper price comparison with other stores.
If I buy a generic Ventolin puffer, the price always seems to be in the same ballpark regardless of where I buy it from.
For things like antihistamines, Chemist Warehouse is notably worse than most other pharmacies: they only stock brand names. They might have a "Chemist Warehouse Exclusive" box of 240 Telfast or something, but it still seems to cost more than generics from other stores.