There is a lot of variability to furnace costs, such as the upfront cost you pay when you buy the actual furnace, the cost to install it, and the gas bill you will be paying from using it. The upfront cost is simple to understand - the more special features a furnace has, the higher the price. Installation costs depend on the area you live in, what is being installed, and the contractor or contracting company used for it. A rough ballpark estimate for the installation cost will typically fall in the $1500-$2500 range. Unfortunately, there isn't a simple estimate that can be given for your gas bill. Too many factors come into play to determine what running your furnace will cost you, such as gas prices, how often it gets used, area you live in, the furnace's fuel efficiency, and so on.