How much should I expect to spend on natural gas?

[Ryan Dossey]

So I may be a tad bit spoiled. I have never had to pay for natural gas. My tenants pay all of their own utilities (except sewer) and my old place was all electric. My wife and I are set to close on our first home (personal residence). House is a 1200 sqft slab house 2/1 built in 78. Gas furnace and water heater. I'm looking for a rough idea of what I should budget in. Home has a wood burning fireplace that I plan to use heavily in winter/fall.