The maximum savings one way with a companion coupon in a roomette on the Empire Builder would be $306, the rail fare portion of the sleeper fare. Round trip applying two companion coupons to both legs, it would be $612.
The maximum possible one way roomette fare for two would be $1806, the current high bucket of $1500 plus another rail fare of $306.
The fares are for the full length between Seattle and Chicago.