Becauae like many things firearms related australia is bleephouse. Not many shops if any at all have direct contact with suppliers overseas. They buy through a third party who buys from overseas contacts.
How much does that affect the price?
Without knowing what people in the US and europe pay, ill give you a comparison on some common guns.
Sig p320 xfive legion sells for $1500us
Glocks typically $7-800us
Cz shadow 2 $1500us
Not to mention the hoops we have to jump through to own handguns. We have to be an active member of a gun club and shoot a minimum of 6 club matches a year just to keep our handgun licence. Long arms are easier to obtain. Then we have caliber restrictions, we cant own anything higher then a 38 super/special. Unless you have a specific collectors licence which is more training and licencing.