Have you seen the videos about how the things start rusting as soon as they leave the lot? And are vulnerable to sunlight and soap? (Kind of like the Wicked Witch of the West!) And the trunk lid is sharp enough and heavy enough to chop vegetables, and the door edge can peel carrots . . .
You could try introducing the concept of marginal cost (in this case, nil, because you have no marginal expense generated by the bulk purchases). But she wouldn’t understand that, either.
Instead, your best approach is to avoid the sunk cost fallacy by ending the discussion. ;)
And how many hours did you have to work to earn that single dollar? Longer than it would take you today to earn $14?