I am a miser as well, and when using the kettles I shut it down when doen to preserve coal. I relight the previous briqs at my next cook, then add new fuel.
When using a WSM, I typically let it burn out unless there is a large amount when I am done cooking.
90% or more of my fuel is KBB. I usel lump when I have it, and when I am doing pizza.
Tough to say how much I use, but I would throw an estimate of less than 10 pounds per week, cooking 3-4 times a week.