Basically, for shipping by sea, weight is barely important. Volume is the most important thing. I forget how much it costs to ship a container (like those big containers you see at ship yards or on trains), but essentially it is little enough that cross atlantic/pacific is essentially free. If you have enough to fill up a container and you have someone who can do the paperwork on the other end, it is totally feasible.
I shipped my bicycles from England to Japan on a partial palette. I can't even remember how much I paid... Maybe $100. And that's for a third party shipping company that came to my door, wrapped my bike boxes, put them on a palette and found space in an unfilled container. The hitch? I had to go to the docks in Japan, fill in the paperwork, do the customs inspection, etc. It took me a whole day. To have someone else do the work for me on that side would have cost $1000.
If you can't receive large shipments, then they have you over a barrel and they will suck the money out of you. Probably there is a business opportunity there...
Order of magnitude: thing "new iPhone" not "new MacBook." If that leaves anyone flabbergasted, yep, that is why containerization is one of the most important technologies in the world.
Since it was assumed that anyone who receives a letter would write back (mind you this was thought up way before online shopping in the 1860s) it would average out, so basically every nation in the world agreed to forward foreign mail for free, assuming it would average out. This only works for things that are send as mail and not as packages.
See also http://fortune.com/2015/03/11/united-nations-subsidy-chinese...