How much does it cost to check in an electric guitar on an international flight from SeaTac?

I'm flying from Seattle-Tacoma International to Incheon (in Korea) then finally to Nanjing (in China), and I would like to know how much extra (unless it's free) to check in a guitar on this flight. I do realize carrying it on is better, but this is just so I am aware of costs IF I am not allowed to check it in. Also, if you can provide some proof or something (I'm 13 and I need to convince my mother that I can indeed transport it and how much it costs to buy a guitar in America opposed to China) to back your statement up? Thanks in advance!