I can't even guess what it would cost to heat my shop to 70 with propane per year. We burned $2400.00 per year heating the house & keeping the shop just above 40 degrees years ago. Now Propane is double & shop is full time business. I'm certain that wood heat has paid for all my "toys" & tools to make it many times over. I love the no guilt feeling of just turning it up if it's chilly.
In terms of cost of wood vs furnace have one word. Truckthreetrailerslogsplitterninesawsmountaimsofchainssawbarsaxessplittingwedgesshedtoholditallgasoilmachetehatchets We have definitely saved money the old furnace was almost $500 a month dead of winter vs the wood being cheap or free. As time goes by it reverses because we installed a 3 stage 98% efficiency furnace and that puppy is like a hybrid car on gas but the wife likes the wood heat so it won’t go away.