Raj,
Congrats on the forthcoming parenthood!! With 3 kidlets myself, I understand about money being tight.
Certainly the HtExchanger replacement will get you through for now, but unless there has been other work done on the unit, everything else is 15yrs old as well. The motors, burners, gas valve, and electronics are all on the downside of their lifespan. You may be begining a cycle of "good money after bad". Most repairs run between $300 and $800 per incident. It wouldn't take long to spend half the cost of a new one.
With regard to the Sears quote, can you fill us in on what brand and model he was quoting? Was it mid or hi-efficiency? Was it a Single Stage, Two Stage, or Two Stage with Variable speed motors?
The Variable furnaces are the most expensive, but they have the quickest payback due to electrical savings. (They only use 80 to 100 watts as opposed to 600.)
If the house was bought as an investment with the intent of turning it over within a few years, you should be able to buy a furnace for far less than $4K. (Or have that one fixed) If you plan to be there long term, seriously consider dropping the extra dough for a good one.
Feel free to PM me.
