I'm trying to make soups (e.g. tomato soups, with some veggies, chillies, etc) and would like to make its cost lowest possible. One problem that I have to solve is choosing the right thickening agent in order to make the soup cheapest possible. Flour seems a common choice, but there is also xanthan gum.  Xanthan gum is more expensive per gram, but looking at the cost per gram is misleading as different amounts in grams are required to thicken a given volume.  For example, only a few grams of xanthan gum are required to thicken a serving. To be more specific, suppose that I have 500ml of hot water that I'd like to thicken, what's the cheapest way to thicken it with a soup-like consistency? There are many more thickening agents than the two that I have mentioned so far, and this complicates the problem for me as I'm not experienced with thickening agents nor soups.  Therefore, experts' opinions here would be really helpful, specially that this question seems not answered here, and my search attempts failed to find any website that answers it. 
An absolutely definitive answer would be based on a formula that takes into account the thickening power per weight of different thickeners as well as the cost per weight of the thickening agent. That's completely unnecessary however because I can tell you without a doubt that the cheapest thickener is wheat flour. I don't have to do any of that work because food companies have done that for me: they keep their prices competitive by getting the most effect out of the least price, and they use wheat flour and cornstarch for soup thickening almost exclusively. Xanthan gum may be used in some gluten free recipes, but it's rare. If it was cost effective they'd be using it everywhere. Of the two most frequently used, cornstarch is double the thickening power of flour, but is far more expensive. The quick checks I did showed anywhere between 10-20 time the price of flour, so at least 5 times the cost for equivalent thickening power. Cornstarch has distinct advantages over flour as a thickener: it doesn't need to be cooked before it's added and it adds a nice gloss, however purely on a cost basis you won't get cheaper than flour. 