Coeur d'Alene Id to Biggs Junction. Or

One possible route is I-90 to 395, cut down 395 all the way to Pasco and Kennewick, then onto I-82 down to the Columbia River. Then you can turn off and take 14 west all the way to Biggs. Alternatively, you can cross the river at Umatilla, and take 730 through Irrigon to Boardman, or just drop down I-82 until it terminates at I-84 and head west to Biggs. Oregon side is faster and has more services along the way (and mountain goats along the basalt cliffs between Arlington and John Day Dam).
Steve