Searching for Great-Grandfather Per Anderson

Recently I discovered a Purchaser's Receipt for my great-grandfather. The receipt is for Elder Dempster & Co., Beaver Line of Steamships. It is dated 11/13/1903. It pays for steerage from Christiania to Spokane, Washington for Per Anderson, his wife, Ida, and their children (Iver, Signe, Harold, Robert, Ingeborg, and an infant son). The amount was for $305 purchased by AJ Freeborg in Spokane, Wa. I have tried unsuccessfully to locate which ship they would have been on, including Ellis Island's web sites. Are there any experts out there who can help? Thanks - Marie Anderson