I think part of the point here is that some commodities may have highly variable prices for discernible reasons - manufacturing costs, supply/ demand, etc. - an

I think part of the point here is that some commodities may have highly variable prices for discernible reasons - manufacturing costs, supply/ demand, etc. - and it makes sense to try and get a good deal. For other products, like groceries, prices are mostly stable so it doesn't make as much sense. If there were rice shortages and your brand of rice cost much more all of a sudden, though, I would expect you might shop around then