What's the most expensive thing, by weight, that you can buy in a grocery store?
Many people reading that question will latch on to the word "weight" and start thinking about meat. Could it be a fine cut of beef or veal? Does your store carry dry aged, restaurant quality, prime beef? It doesn't matter if they do, the answer isn't meat. Not even if your store carries imported Kobe beef at well over a hundred dollars a pound.
Maybe weight was misdirecting and it's a liquid. Can grocery stores in your state sell wine? That doesn't matter either. Even if you shop at a high end yuppie store with bottles of wine that go into hundreds of dollars for 750 ml, you're not in the right section and you're still an order of magnitude off.
But bottles are the correct container. By weight, the most expensive thing in a typical grocery store are the spices. Even a common and easy to grow spice like oregano can sell for the equivalent of over a hundred dollars a pound. Yesterday, I calculated saffron at my nearest store at about twenty-two thousand dollars per pound, hough I doubt as if all of the bottles of all of the brands of saffron in the store would have yielded even two ounces. For comparison purposes, gold is currently selling for about thirteen thousand five hundred per pound.