I use less than 10GB per annum on an infrequently used iPad.
Before Roamless, the cheapest plan I can find that will accomodate that usage is through Aldi Mobile at $95/year for 30GB. Prior to that, Amaysim had $60 for 60GB for a 365 day SIM which was significantly upvoted here (https://www.ozbargain.com.au/node/776176).
Roamless (https://roamless.com/) claims credit never expires, and its charges for AU data are $2.86USD/GB. That's $43 AUD per annum for 10 GB, with no ridiculous expiry terms imposed. Even better, it'll work on both Telstra and Optus in Australia according to the rep (https://www.ozbargain.com.au/comment/14964403/redir)
Am I missing something? This seems to beat all Australian prepaid SIMs (and every eSIM for roaming data I've found) for infrequent, low-data usage.
Hotspot from your hphone?