Office Depot takes $50 off customized Post-it Note orders of $50 or more via coupon code "67264205". Plus, all orders of $50 or more (before coupon) receive free shipping. That's the best such deal we've ever seen for customized Post-it notes. Sales tax is added where applicable.
A best bet is the Post-it Note Economy 4x3" 10-Pack (pictured) for $16.99. Add three to your cart (30 total) for $50.97, and apply the coupon code above for a final price of 97 cents. (You may need to add these as separate items in your cart, rather than ordering multiple packages.) With free shipping, that's $50 off, $0.03/note, and the lowest total price we could find. You can add two short lines of text.