A friend of mine bought an old rock building in a little town south of here to store his rust buckets, one of those that had seen many different businesses through the years and was pretty much gutted other than plumbing to the rest room and old electrical throughout. An HVAC buddy knew a guy that knew a guy who stockpiled takeout furnace units from residential homes, swapped pieces & parts to make one good unit out of two or three, and sold them really cheap. Friend bought a big one, set it at one end of the big open shop area, slapped a big sheet metal elbow on top and ran a line to it with a thermostat off to the side. No ducting other than a big elbow on top pointed to the far end of the building, about 7' off the floor. Don't know why a guy couldn't do that with an AC unit, too. Not pretty, but it works if you're OK with some drafts....