Many sellers in the UK and USA have been opted into the Global Shipping Program.
It is expensive and slow.
Some sellers are unaware they have been opted in and that their postage is showing as such for International buyers.
You could message the seller and ask if they are prepared to use the standard postal service but you need to respect them if they don't want to.
That seller is using the Royal Mail International Signed For service....not the Global Shipping that is so expensive.
Either the item is deceptively heavy for it's size or the seller is charging high postage because he can.
At the end of the day, if you don't agree with the postage costs, you need to move on and find another seller. Some sellers seem to be unaware that fees are charged on postage as well as the item. I still occasionally see a $2 item with a postage cost of $100. In actual fact the item is probably $100 and the postage $2, but the seller thinks they are saving on fees by listing it the other way round. Most of us stay away from Global Shipping. Not only is it slow and expensive, but I believe they do not pack the items sufficiently for overseas travel, and a lot of the items get damaged as a result. I am going on hearsay here, I have not used it myself and don't intend to.