A GameCube will only fix in a Large Flat rate box. I have sold two my self and they did not fit in a Medium box. Just an FYI. The thing is, you can send it Media shipping which is cheaper.
you can fit that in a medium flat rate box thinks $13. about thats your best bet for shipping this and you get free tracking with it'' i have one i'm going to be posting up today mine has the box with it so i haft to use an large flat rate box