Peter, check out
www.tirerack.com. This is where I expect all people will be buying tyres from. Craig has used them before. You can use Longbeach, CA address to work out shipping from them to container.
The only missing amount is cost for your use of container.
Normal duty is 10%, then 10% on top of that for GST. You also have to include shipping costs when applying duty & gst.
You can play around a bit and work out roughly if it is worth it.
For small items, worth less than AU$250 delivered probably best to send directly here as they won't attract duty or gst. And the extra shipping costs would be offset by duty & gst savings. I've got to buy some polyurethane bushes, but these would be cheaper to buy directly as shipping is relatively cheap.
There is a bit more risk and hassle buying this way from US. You've just got to weigh up whether the savings are worthwhile.
Peter, you should also look at aluminium radiators in the US, much cheaper than here. I'm thinking about a cheap AFCO radiator myself. Which I know have been bagged a little here, but work fine for people with more stock applications.