I've had a sand paper pencil sharpener taped to the top right corner of
my drawing table for many years now. They can greatly extend the life
out of your pencils and nearly all art stores carry them. When a layer
gets full, you can just remove it and there is a clean layer underneath.
They do produce lots of dust though. I figured out over time, if you
put a bag over the sharpener, it will keep your area clean.