Stack with $20 off $200+ Spend (Exclusions Apply) @ Student Edge or Student Beans to get $30 off $200+ spend.
Further stack with Earn $20 - $70 Bonus Store Credit When Shopping @ The Good Guys
If you want to be more adventurous and are targeted with CommBank Rewards: Get $30 Back with $300 Spend @ The Good Guys - Buy gift cards with CBA card and then when buying an item part pay $50 with AfterPay to get $10 off.
Do they sell JB gift cards?