Quoted from Fytr:
I wonder if a padded envelope would be better/cheaper?
Possibly. But the cost between USPS envelope and a USPS box is around a dollar difference. I don't think postage would be very much less, but don't know for sure. The same box I use (with less than one ounce weight ) to ship to Canada for the $10.00 only costs $3.50 to ship anywhere US.
For my Catacomb ball gate wires, I feel safer with the structural rigidity of the small box. But that could be misplaced faith, though.