Sometimes Flat rate boxes or envelpes are not cheaper. I just sent an envelope of papers and a wall hanging to my DH in a brown envelope and it cost me 2.49 sent priority. My DS sent me a gift in the 23.50 FR box because it would not fit in any smaller and the box was half empty. I am sure she could have sent it for less money is using another box. Po usually gives you the cheapest method which is usually priority.