Propane Question: Help!

Help! We found a house we adore. It's perfect in every way but one--it's heated with propane. I'm trying to figure out how much it'll cost to heat. (The realtor is looking into getting the official records, but until then...)  Does anyone out there have experience with this?  The house is 2,400 square feet, plus semi-finished walkout basement. The furnace is only a year old. The various on-line calculators I've tried give wildly different answers (and last winter was extra bad for propane prices). Any ideas out there in LJ land?