Oh, even simpler: cheap sous-vide circulator and rubbermaid "tank" for the outer water bath, tall glass pitcher for the actual coffee, cotton "tea sock" to hold (and filter) the ground coffee in the pitcher. Most of the complication is that it needs to weigh enough (or be braced) so that all of the coffee is submerged, without the pitcher starting to float... and if the pitcher has a neck make sure that the coffee absorbing water and swelling doesn't get stuck inside the pitcher...