Thank you everyone for all of your help, every little bit helps! I have received more quotes recently, one as low as €2735 for a wooden box. It is a good point that the bigger the box be it PVC or wooden the more the dog would be tossed about.
I am going to get him his rabies shot and take the first step to bringing him, despite not being sure if I am going to bring him yet! I am trying to get family to take him in at least until I settle in Oz!
I have to stay in Joondalup for 3.5 months and then move south of the river (not sure of the location yet) after that. So it's all very new and complicated for me at the moment.