International parcel air post rates are around 200 RMB for one Kg. Check at the post office counter (you will need a translator if you cannot speak Chinese) for the current rates at the time you wish to send mail.
There are international courier companies operating out of Changchun. It may be possible to get a favourable quote from them.
Airmail takes around 10 days. Surface post up to 3 months if by ship. Couriers can deliver internationally in 3 to 4 days. E-mail is generally the best option for sending correspondence. Fax services may or not work well, depending on the phone lines in your area.
It is advised that you attempt to receive mail at your work office address or through a courier or counter mail. To any other destination in all likelihood there will be no delivery, your mail will simply "disappear."