1 cord of firewood BTUs = 215 gallons LP BTUs. I'm probably using about 600 gallons of LP to heat my house. $3 per gallon, roughly.
I'm already burning a bunch of the wood in a very inefficient fireplace that, while great for ambiance, sucks at actually heating the house. The same firewood, plus some unknown additional quantity (guessing a cord or two), in an efficient heating appliance, would dramatically cut the need for propane.
Even if it ends up being 3 or 4 cords, that's fine. My math has a lot of rounding errors. For the sake of discussion, roll with it?