and before anyone thinks that I am a “GSP apologist”, take a look at:

https://community.ebay.com.au/t5/Buying/GSP-stupidity-documented-on-this-thread/m-p/1708839#M55075  (But please do not post on that thread as it is old).

There is a post on there that explains the GSP shipping can be high when the seller has not included the dimensions and weight of the item, resulting in the pricing algorithm using an averaging of items listed in the same category.  For the low weight item this means that the price is being determined by higher weight items in the same category (as mentioned by padi).