Having a new furnace, duct work, windows and doors will all help REDUCE the AMOUNT of propane you USE so the only relavent factor is the price per gallon you'll have to pay. Shop around for propane dealers in your area. Most will have budget plans and some may even offer you a program where you can pre-buy your fuel in the off season to carry you through your next winter thus locking you in at a much lower price than what you'd pay during the cold winter. Go to www.nypropane.com to search for dealers in your area. Reputable dealers will belong to their state association and the associations internally police the members to weed the bad apples out.
Source: 32 years in the propane industry