Optus is currently offering 10% off their 4G home internet plans:
500GB/Mth + B818 4G Wi-Fi Modem for $67.50/Month for First 24 Months
200GB/Mth + B818 4G Wi-Fi Modem for $58.50/Month for First 24 Months
If you decide to cancel the 24 month plan, you will just need to pay out the remaining cost of the modem.
If 5G Home Internet becomes available at your address you can switch without paying any plan cancellation fees.
Edit: Offer ends 30/5/21.