To china, I have no clue, but it costs me about $40 to ship a Flat Rate to Spain, if that's any help to you. If you use any other box than the flat rate, it will cost a TON more.
Izy might be able to give you the exact price if she still has the box I sent to her.
I just did a search...go here
http://ircalc.usps.gov/
You can calculate the price.