Sony WH-1000XM3 Wireless Noise Cancelling Headphones - Black / Silver $322.70 + Delivery (Free with eBay Plus) @ Allphones eBay
Allphones eBay Store currently has 8% off at checkout, which also stacks with the 20% eBay promotion
Subtotal (1 item): AU $438.45
Discount: -AU $35.08
Vouchers/coupons: -AU $80.67
Order total: AU $322.70
Update: Appears Allphones has removed the listing and the 8% off at checkout promotion.