Look for a kit of memory simular to this.
Newegg.com - OCZ Gold 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model OCZ3G1600LV4GK - Desktop Memory
If you could link us to the store your planning on shopping at we could give you more direct suggestions. And a budget, how much cash can we spend
I am looking at these shops:
Scorpion Technology: Online Computer Hardware & Software Store in Australia - Scorpion Technology
Computer Hardware & Software Australia | Techbuy Australia
Roughly $2000 AUD , currently im at about $1500 with original list.
Cheers