In case you’re still confused why the cheap product got hit so hard, it’s because the pull/pack/weight fees are flat rate, so it’s the same rate for your 6 buck item as your 15 buck or a 100 buck item of the same size and weight.
Think about it. It costs you $2.61 to ship 6 postcards USPS; correct? And probably about the same for 12. The post office didn’t say, “Oh, this is a cheap item; we’ll reduce the fees.”
Amazon’s pull/pack/weight based fee is about the same as if you shipped it yourself; only difference is if you did ship yourself, you would charge a shipping fee. With Amazon, you get no shipping concession, so you have to either roll it into your item price or send pricier items.
It is only the commission that varies, since it’s based on a percentage.
I send a few fast moving $12 items, but usually it’s $15 to $35 items that I send.