I never sold possessions to buy more sugar...
Sugar? For snobs anyway. Corn starch for the masses.
Your example also doesn't really hold up because people typically don't process cocaine in the way they do with sugar and other carbohydrates. In your hypothetical scenario, we might see people consuming large amounts of pure sugar (or artificial sweeteners), but they wouldn't go to lengths of baking bread using it.
Not as cheap as sugar, but probably as cheap as coffee. Coca and coffee grow in the same climates, and in recent years the cartels have bred varieties of coca that grow outside of the traditional climate as well. Imagine what modern agribusiness would be capable of.