Assuming it's the US we're talking about, the federal minimum wage is $7.25, which means that if every worker involved is paid at the minimum wage, you incur a cent of labour costs every 4.97 person-seconds. AFAICT, most Amazon workers are paid substantially higher than the federal minimum wage. And that's just labour costs.

While Amazon is efficient, "fractions of a cent" is probably the wrong order of magnitude for even the most efficient order.