Could have been cheaper at previous eBay deals but I think it's best you can get for now.
You can purchase David Jones gift card at 10% discount from many different sources. (Guide: https://www.ozbargain.com.au/wiki/discounted_egift_cards)
I got mine from RACQ rewards which was accessible immediately. Not sure about other rewards.
Cash Rewards 10% cash back deal ends tonight.
https://www.ozbargain.com.au/node/375656
Note - Cash back is actually 9.1% as it excludes GST.
So around 18.1% discount after gift card and cashback.
This is not limited to Galaxy S8+, they have S9 S9+ S8 as well or anything else they sell but not eligible for Apple and some products (you can get gift card discount but cash back is excluded)
S8+ 949 -> 777
S8 999 -> 818 (more expensive than S8+)
S9 1199 -> 982
S9+ 1349 -> 1105
S9s link: http://search.davidjones.com.au/search?ts=m&w=Galaxy%20S9&is...
Hope this helps someone.