None of these "experts" answered your question, did they?
I am an Illinois contractor, and the pricing in your area is similar.
Without knowing the size of your house, I can give you a range: budget
between 5-8000.00 US for the work, maybe as much as 10000.00 if the
ductwork needs extensive repairs and alterations. "Ancient" forced air
sustems are usually severely lacking in cold air return paths, and that
can run into some dough. A good rule of thumb is 2.50-3.00 per square
foot of living space for your heating plant. A better way is to make an
offer contingent on replacement costs being known before closing, and
adjust the contract accordingly. Your attorney can guide you there.

Good Luck!

Glenn
http://www.goalelectrical.com

wrote:
I live in Missouri and am a first time home buyer. The home we are
looking at buying has an ancient furnace and central air conditioner.
I'm having a lot of trouble just finding what a new furnace and air
conditioner might cost. Can anyone give me a range for furnace and for
ac in US dollars? Thanks