One thing to keep in mind with shipping, it's not just the weight but the thickness. If it's over 1/4" thick, the PO may consider it a package instead of a letter and then different rates apply. My very first envelope I took the PO and they wanted to charge me over $2 for it. I took it home, put it in a slightly bigger envelope so it was thinner, and then it cost 70 cents to mail.