I sent 2 boxes 2 weeks ago, I think combined they were 40-50 lbs in weight and it cost me close to $100. But it was all my heavy winter coats and sweaters etc, so I thought it was easier to ship than replace. The lady just told me to double tape the seams, and I used packing tape that we use to mail things from my office. I'm just re-using sturdy boxes that our supplies arrrive in - ones with no rips or bent places. She told me to think about all the weather it might face - humidity, dampness, getting rained on etc.
I've got 3 more boxes to go, then my pc and that's it. I went the surface route so will take about another month to arrive at the least. I used the sheets I was taking to wrap my pots and pans so they'd not scratch.. that sort of thing.