Costco has 100 stamps for $39 after checking out via the Google Express app and applying coupon APPSAVE20.
Open the link via the Google Express app and apply the coupon before checkout. You'll need to add your Costco card of you haven't already done so. Shipping is free.
Not as good as the previous deal, but still $10 off, bringing the cost to 39 cents each. Stamps will be going up to 50 cents each on the 21st.