Follow the link for the rates charged by the post office. Also they wrap your parcel in cloth for no reason and charge you almost RS 500 to do that. If the size of your parcel is bigger, this can go upto RS 1500. This money goes to peons and others who do this sewing job and probably is shared by everyone who work there at the end of the day.

There is customs office at the post office in Sundhara which does EMS, and the officer there will assess your parcel and may charge you export tax. If your parcel is sent as gift, you may end up paying nothing.

Also if your items are worth over USD 200, you may have to pay customs depending on what you are bringing to US. There are products that qualify as exemption to customs from Nepal.

http://www.gpo.gov.np/EmsRate.aspx