Hi Rob,
Google tells me that USD$414 is AUD$538.78
The sweet spot for me (freight costs) when I bought tyres from Jake Wilson was 3 pair, though I haven't bought tyres for a couple of years.
Personally, for such a small saving, I would buy locally.
I have had to buy tyres on two different trips away. Both times (Alice Springs and Port Augusta) there was only 1 rear tyre left in the shop so fortunatley I didn't have to pay for extra days accommodation while waiting for a replacement tyre to be shipped in. You can be lucky.
If you have the room just carry a rear tyre. It is going to go first, especially when towing. Your front tyre may last until you get home. Otherwise once you've replaced the rear tyre purchase a front tyre at the next major town and carry that. This way you'll only need to carry one tyre at a time.