A letter sent anywhere in the US is $.44 as long as it is under 1 ounce.A postcard costs $.28 as long as it is under the maximum size: 6 inches long by 4 1/4 inches high by .016 inch thick.
48 cents i believe but after what e-mails did to the post office it should be 48 bucks.only thing cheaper would be a post card but then everyone could read it.Is that what you meant by post-secret?