Cez, on one account I sell second hand books. Many of them do go for the $4 - $5, so similar price range to yourself and also needing to be sent in 500g and 3 kg satchels, or even the flat rate boxes.

The way I figured it was that every seller of a particular book was in the same boat as myself, in that they too were faced with incorporating the increased price into their product sale price.

So it is still possible and in most cases entirely realistic that it will be worth it as you can and should pass this price rise onto your customewr.

It is no different to a B&M store rising their prices when petrol prices or other supply chain costs increase.

It's just that we are not used to seeing the break down of expenses in a real store, so we don't really scrutinize what the price rise is for.