For that much money I would put towards a new furnace. Maybe you can get a lower price. I would call a couple other contractors and see if they can do that for less.

Replace it!!

Your throwing good money towards bad. At that price, you're at approximately 1/3 of the cost of a new one.

Have your contractor heck it out .. last year I replaced 4 Bryant furnaces for this same reason, 12, 15 and 18 yrs old. Don't even mess with the new heat exchanger, you end up with an old furnace with a new heat exchanger. Carrier credited $600.00 toward the furnaces and $450.00 labor for the install. Trouble is they replace it with the same identical piece of junk. And the contractor will wait for three months to get credit.

Snoringcow, What would a new 100 BTU Carrier cost? In Maryland, outside Washington, DC. This is easy access in basement, which is on ground lavel straight in from driveway, no stairs.

I know a contractor for this work, thay are quit professional & experts of furnace.

Here is a link that might be useful: Alfa Mechanical