$132.54 shipping to UK.
You might want to contact them directly about that. That sounds like some sort of an automated shipping cost generator, and seeing as S&S sells a lot of Harley parts world wide, I'd be willing to bet that the T-shirt may be miscategorized in their shipping system.
Good Lord, I had a whole K-series MG/Rover engine shipped over from Manchester to Milwaukee - 200 lbs - for $700.00, and that included a pallet. A T-shirt fits in a mail bag, and I'd be surprised if the total cast would be 10 pounds Sterling.