In our little local Tesco this evening, I was down at that end of an aisle where the spices are stacked. And I saw one of the most egregious examples I've ever seen of the fact that much of what you buy is not strictly priced by weight, but often by how much hassle it is getting it to you.
38g of Hot Chilli powder. £1.36 1000g of Hot Chilli powder. £2.99
Yes, for little more than twice the price, you can have over 25 times as much.
(I'm also not entirely sure why the place is selling Hot Chilli powder by the kilo. Perhaps they've heard that a P Morwood may visit one day.)