I see. You make good points about Whitman, but average cost after aid tends to be lower at Whitworth than Whitman (which, of course, could be a result of more students without need attending Whitman).
In any event, it may be worth running Net Price Calculators at both schools and getting the financial pre-read at Whitman if OP’s son likes it. I know students from both, all great people, but different vibes. Whitworth’s Presbyterian/Christian values may appeal more to OP. I have visited Whitman and loved it; it felt a little like the Carleton of the West to me.