Where can one get cream of tartar for a reasonable price?
Everywhere I look, it’s extortionate.
Cream of tartar is a byproduct of the wine making industry and if there is not much wine being made the price will go up. COT is usually used to add a bit of acid to a recipe so you can substitute other acids such as lemon juice, cream cheese, or even sour milk. The substitutes may add tartness as well so you will need to balance that with a sweetener and they may not be as consistent as the pure COT so some experimenting is needed. BTW Baking Powder contains COT so if you don't need much that may work as well.
I have several places. San Francisco Herb Co. at 5.85 per pound, King Arthur Flour Co. 5.95 for 3 oz. or the Grain Mill of Wake Forest, NC at 27.95 for 3 pounds. I have not used the first one but it was recommended to me.