Factory Ammo prices, per pk/20:

.375 H&H ammo:
PMC cheap [conventional 270 gn bullet] mid 40's
PMC premium [Barnes X-bullet, 270 or 300 gn] about $90
Winchester/Remington: about $75-85

.416 Rem: Haven't seen an Aussie price lately, but Federal and Remington run US$85-90 from discounters in the States.
So double that, and you'll be fairly close to an Oz price. As I mentioned elswhere, they're expensive. Still, not in the same league as .470NE though - recent reports of $400/pk in Sydney!