I would say the prices in OZ seem to be about the same or maybe a bit more than the prices you listed. In different parts of Australia ,the availability would be different. Where I live ,it is stocked and in Darwin it would be stocked. But in areas where there is no big game you would have to order it in or reload from components. Since the big bore stuff is usualy very expensive or hard to get ,reloading is even more viable than with cheap easy to get 223s or 308s. As for the amount of big bore ammo we shoot in a year. WEll some people would go through only a few rounds if they are scared but then some of the people on the board ,my self included would go through 500-1000 shots or more. Of course most of this would only be at paper or playing in the bush. With my 458 Lott for example, I have been experimenting with various loads with bullets ranging from 250 to 550 gn (will try some 600s soon) and have been playing with cast bullets so I have fired probably 300 rounds in 3 months.
AS for never shooting from a bench ,well a lot of my shooting is from a bench ,but its only a 458 Lott. It is much more comfortable shooting off hand ,but the bench is good for sighting in and experimenting with loads. I dont like firing the 460 weatherby of a bench ,even off hand is a bit much for me. Some people on the board have things like 585 Nyatis ,I dont think they will spend much time at the benchrest.