Since water is specifically cheap (at least in my part of the world), maybe you should have price per dry mass (would work for food and cleaning agents) but tha

Since water is specifically cheap (at least in my part of the world), maybe you should have price per dry mass (would work for food and cleaning agents) but that would probably mean they'd add sawdust or starch or sugar. So we could also add those to the "cheap ingredient list" but of course it's a never-ending battle and likely not to the benefit of the consumer. I suppose we're actually dealing with a price distribution so maybe a possible solution is: a graph where X is the procurement price per ingredient and Y is the percentage of the product that is composed of things with ingredient price <= X. You'd want to have as small as possible an area under that curve but then the question is the procurement price and we've gone full circle.