Indeed, at high volume the cost of stuffing/testing is comparable to the cost of the part ~1mil=$/1000. Actually, cost can increase more significantly if the number of different components increases too much (and inventory is more annoying) so it may be cheaper to stuff 2 or more of the same component rather than have more different values. Of course nobody really cares about this, if you're making less than ~100k/mo since setup costs dominate. A single line can do ~250k/mo running 24 hours. If the line runs less than 8h/day, they'll turn it off and/or switch to a different product on that line each month, which can cost multiple $k.