YMMV depending on the efficiency of your fossil fuel furnace compared to the efficiency of your wood stove. Also have to factor in the huge swings in fossil fuel prices during the past two winters. But this is a great starting point.
For me, I know my old inefficient 1982 LP gas boiler burns 400 gallons in a cold month. My wood boiler will gobble 3 cords of aspen or munch 1.25-1.5 cords of hardwood in a cold month.
400x$1.19 is $476 (this year)
400x$4.50 is $1800 (last year)
476/1.5= $317 per cord hardwood equivalent or $476/3=$158 per cord aspen equivalent.
My maximum cost per cord if I allocate fuel, chain sharpening, and bar oil to haul hardwood from my hunting cabin is about $35 per cord. But I never make a dedicated trip to haul wood, it's always in conjunction with something I needed to do up there. If I had to buy $200 per cord hardwood (compared to $1.19 propane) I'd just throw the money to the gas man as feeding the fire and hauling wood in all month to save $175 isn't worth it.
Now if I replaced the gas boiler with a new efficient unit those figures would likely cut in half.