The British Corner Shop is the cheapest site on the web to get items from the UK you might not be able to get here. At the moment they have 10% off delivery, which is £17.99 to Madeira before the discount.
You can order up to 30kg in weight which does include the packing etc. and as you add stuff to your basket you can see how much the weight is as it’s added.
I contacted British corner shop to ask why delivery is so expensive to Madeira when it’s only 11.99 to Mainland Portugal, and they just replied that they are the cheapest you will find, which I agree with, and they are already subsidising the cost by £10.00