When I know my potatoes are going to go bad soon, I cook ’em up. I bake a whole cookie sheet full of cubed/seasoned potatoes, slice them and bake them in foil, or boil a bunch on the stove and mash them. Then we eat some and freeze the rest. They stay for a good month or more.
Speaking of which, I have to do that more often. Comparatively, potatoes are pretty cheap as a side dish.