If you don’t buy the treadmill, you don’t save money on the real estate you already own. It either goes unused or is used for a different purpose. Is this really the right way to think about the trade offs?
Makes a lot of sense if you're space constrained, could see yourself getting space constrained in the future, or value open space. Even then, though, if you needed the space for something else, you could recoup all of the real estate cost and some of the cost of the treadmill by selling it.