It varies quite a lot depending on what sort of item it is, just google UK (item name) import duty. You've also got to consider shipping costs and times, I bought a GoPro from canada which took almost two months to get here with standard delivery. Fortunately I didn't have to pay any import duty which is usually high for electronics because the seller marked it as a gift, meaning it wouldn't get taxed. I wouldn't ask bigger companies to do that sort of thing though as its a little shady.