https://www.costco.com/ Select Costco Members: 1-Time Use Coupon Code Valid for $100 Off Online Purchases $500+. Coupon Code is Emailed to Eligible Costco Customers. This coupon code is for Eligible Costco Members only and sent via Email. Email Subject Line says: Exclusive Code: Get $100 OFF An Order of $500 or More on Costco.com! The coupon code must be entered in the promo code box at checkout to be valid.