Was looking for a cheaper price than Target and found Big W were selling them for $52 each (opposed to Target's $55). Thought that was significant enough, especially for those buying both.
If you're a first-time buyer like myself, remember that both games are completely different experiences story wise. More importantly however, is Conquest is aimed at expert players while Birthright is aimed at everyone else (to the best of my understanding, my apologies if that's not 100% right).
Also, don't forget that if Big W isn't your cup of tea EB Games and JB HiFi will pricematch. That should either save you some petrol or earn you some carrots.
Links:
Fire Emblem Fates: Birthright
Fire Emblem Fates: Conquest
EDIT: Thanks to Max Power for pointing out that if you want both and don't care about physical copies, once you buy one of them you can purchase the other one digitally for $26 Australian (after getting a couple of chapters in).
great find OP!