Using the recharge page in your koganmobile account, the small 365 day plan is $164.20. Buying it as a voucher code via this link saves a $1 per month, working out to $12.50 per 30 days.
Valid for new and existing Kogan Mobile customers. Discounts available on Kogan Mobile Prepaid SMALL, MEDIUM, LARGE & EXTRA LARGE 365 day plans, including recharges, purchased before 11:59pm AEDT 31/12/2019 unless sold out prior or extended. Discount does not apply to subsequent recharges. Personal use only. Not available for commercial or resale purposes. Discount cannot be used in conjunction with any other promotional offers. Not transferable and not redeemable for cash. T&Cs and Fair Use Policy apply.
If you want 8GB instead of 3GB for $1 extra per month, see this link instead.