I received this by email so I suspect it's targeted to anyone who's had a paid subscription before. I tried to make the link generic but every time I did it only went as low as 60% off, so you'll likely only be able to use the targeted link to get the full 75% discount. This is also direct from Bitdefender so you aren't dealing with a third party.
Prices are as follows:
Antivirus Plus 2019 - up to 3 devices / 1 YEAR - AU$17.49
Internet Security 2019 - up to 3 devices / 1 YEAR - AU$25.00
Total Security 2019 - up to 5 devices / 1 YEAR - AU$30.00
Add their VPN Premium for AU$49.99