I tried that too. It is my favorite way to ship things. Can't beat $6 for priority and something large. Lol However, sadly they are too big to fit. They do fit in a medium flat rate box though.
My husband wouldnt be too happy with spending $12 on shipping a pair of shoes lol (he doesnt really understand how shipping works...at all) and I usually ask for $6.20 to cover all fees :)