EDIT: I've changed the link to the stock sold by Amazon AU instead of Harris Technology as their item is now estimated to be delivered 25 Jan, where Amazon AU item is usual couple days. If you want to save $1.50 but wait for delivery, their item as available here.
https://www.amazon.com.au/dp/B00A0VBPLM
Decent price for these basic powerline ethernet adapters. Good idea to buy these from Amazon for easy returns as it's pretty hard to know if these will actually work if you didn't wire your home yourself and performance can vary room to room.
Link posted is shipped by Amazon but sold by Harris Technology, however it's also available sold by Amazon for a couple dollars extra.
https://www.amazon.com.au/gp/product/B00A0VBPLM/ref=crt_ewc_…
Do these work well in old houses with older wiring?