My experience is that you will buy it cheaper in the US than Australia. Given the quantity you are wanting, I would approach the manufacturers or wholesalers direct. Either way, you're up for a reasonably large bill. Another concern which I am sure you will have, is the cost of transport following your purchase. I bought from Defender (a little less expensive than West Marine @ US$1300 for 500') Samson XLS Yacht Braid
The weight of 3/4 braid is 90lb per 500'.
Also have a look here Yacht Braid Rope Promotion-Online Shopping for Promotional Yacht Braid Rope on Aliexpress.com
and perhaps here Recreational Marine
It is also worthwhile looking on eBay (Aust, UK, USA). There is plenty of braid at very good prices although it can be difficult to find 100m reels.