'Robots n stuff' is a rather broad subject for Japan. More than likely what your friend will see are Gundam models. For 1/144 (HG) stuff you're looking at around 1000~2000yen. The bigger the scale the more expensive they are. Plus your friend will only have so much suitcase space.
HLJ.com always lists the msrp yen cost so have a look around there if you're really curious. If you want something unique tell your friend to go to Diver city in Odaiba and pick up some of the exclusive stuff at the Gundam shop there.
I'm not sure how it is in Australia but if you have to pay customs it will add some $$ to the final cost. Still for me, it's cheaper to buy Japanese branded tools and kits from there than local, even some European brands are cheaper there (plusmodel stuff for example).
Does Aus have a VAT like England? Whenever I hear about the Brits ordering from luckymodel or hlj it sounds like that VAT really pounds them in the rear with taxes.