Generally, it is cheaper to get a new split air conditioner installed compared to installing duct work for central ac. The labor and material for ductwork, including the cost for central ac usually surpasses the cost to get a split ac, and install it. I mean it would make sense to do with a central ac if the ductwork is already in place, but doing it all over and on top of that buying a central ac, I personally think thats too much, especially when there are great systems such as split air conditioners.