I'd look at the long expiry plans on the optus website. Click here
A recharge of $30.00 or more on the Optus Prepaid Long Expiry plan will get you pay as you go phone calls/texts/data with an expiry period of 186 days.
A recharge of $60.00 or more will last you a whole year.
If you have any questions, shout out 🙂