Does this exist? A mod to, for example, allow you to go to the spy's table to create a potion and allow you to make one you don't have the ingredients for, at the money cost of all the combined missing ingredients?
Not to my knowledge. I'm actually working on something, where this feature could be included, so I'll have a look into it if I find the time, but I can't promise anything. Already got too much that I want to do, but not enough time