I've been considering buying a guzheng (Chinese Zither) in kunming. The only problem would be shipping it back to the states in a few months. A Chinese friend suggested that I ship it via slow boat. Does anyone know anything about this? Can this be done from Kunming? (we're not exactly a coastal city.) Approximate cost?

My musician friend would only fly with their instruments. The cello guys always have to buy an extra plane ticket. I would worry about it getting damaged. It's not a super structured instrument and the moist salt air from shipping by sea can't be good for the wood or the string connections. Guzhengs are not too large to fly with.

Alternative, is get a box that is at least 6 inches bigger all round.
Then put in the in a large plastic bag to cover the bottom and spray into the bags that aerosol expanding construction foam. The quickly bed in the instrument before the foam expands and sets. You may need to hold the contents down to allow the foam to expand around the sides. Use two smaller bags for the ends and to the same. Then use a another large plastic bag that is bigger than the space remaining, and use the foam in this bag too. Quickly loosely close the lid so that as the foam expands it fill the spaces around the contents. When it is set the lid will have raised, open the box and trim off the excess with a bread knife or cheap wood saw. The whole lot should now be one solid mass with the contents not being able to move.

Note, remove strings. remove any fragile parts (bridges, etc) if they can be removed first. If not make a small box out of cardboard to cover them. If there are any sound holes or other areas where the foam filled bag could squeeze in, then cover these with thin cardboard. This can be stuck down with electrical tape which should pull off later without leaving a residue.

The method above is how I have packed wooden models for shipping.

Since you haven't bought one yet, why not do so once you arrive home?

So far I never sent an instrument out of China, but I had two guitars sent from overseas to China. One was send from the U.S. to China via USPS / China Post and the other one from Germany via DHL / China Post.
Both instruments arrived here in perfect condition. They were packed in the sturdy Gig Bag or in the Hard Case inside a simple carton box, which, however, was filled with material to prevent the cases from moving inside the carton box. I wonder if it would work the other way around as well. Shipping time was in both cases around three weeks. Both shipments came by air with low priority, that's why it took so long. Definetly refrain from sending it as checked luggage. This way I ruined my 12-string guitar, although it was packed in a hard shell case, designed for this purpose.

Definitely send it by fedex or some other respected service. I've had many things go missing sending from China and vice versa cos i thought it would be okay not to pay the extra.

At least with fedex etc it will be covered if anything happens to it.