As you know Toys'R'Us currently have 'Buy one get one 1/2 Price on LEGO'. If you use the PAYPAL 'Buy one get one 1/2 Price' Promo Code then it deducts the highest item and makes them both half price (hence buy one get one free)
Note: It only works on full price items and I found that delivery skyrocketed for a lot of items to Perth
You can try 4 or other even numbers of sets to save delivery fee as long as they are pairs of each set (or just pairs of same price items?)
e.g. I bought 6 sets, (two copies x three different sets each), pay half price of each set plus delivery fee.