[Sangetsu]

I mailed several boxes of personal items to Japan before I moved here. The boxes were similar in size to the one you are describing, and they cost about $100 each to send by priority mail.

Flying with an oversize or additional bag can be costly. I checked-in a bicycle case in addition to my 2 checked bags, the bike case cost an extra $150, and had they known there was a bicycle in it (I lied and said it contained camera equipment), it would have been an additional $150. One of my suitcases was deemed to be overweight, so I had to pay a further $75.