You can go by air freight, which is where they put boxes on regular passenger planes, and its cheaper than express post and around the same speed. I sent a set of coilovers to the US that way for around $500 (47kg total), cheapest i could get anywhere else was around the $1k mark. I had to go through a freight forwarder though (cant remember the agent i used)
Another type of freight you might like to try is something like excess baggage - Plenty of companies can be found by Googling the term.
If you shop arround, there are actually some that are quite reasonable (cost wise).. Might be worthwhile moving a few things with that method and the remainder by sea if you not that fussed about the shipping time.
If you do find some other good ways, do post back on here. I am moving there next month for a 6 month work contract (as long as my visa comes back in time lol)
Btw, be careful if you are going on a tourist visa and intending to work; they are supposed to be pretty strict on illegals. Visa process is sllloooooowww too, so dont leave it till the last minute like i did
As you said before your in no rush. I would recommend ground shipping (but takes a long time maybe...3-8 weeks to japan). not sure which companies are available to you, Fed Ex has always worked well for me.
If you use AUS POST, there is no sea mail for ASIA.
but what u can do is. air mail it. then insure it for the minimum $100 just so you get a tracking number and someone has to sign for it at the other end.
lol i know the deal with the visas there, and how unhelpful the japanese consulate is here in melbourne
Luckily mine is all being handled by a professional in Tokyo (though i had to translate my resume for them!). Now all i can do is wait... I thought 3 months was plenty of time, but i'm starting to get anxious