Have a Carrier Weathermaker SX furnace, it locks out at night a few times a week. Cleaned the trap out, repairman says need new heat exchanger. $750!! Does this sound right? Furnace is about 15 years old.

Yep,, I would consider a replacement furnace(something to think about)

Money is kind of tight, bad move getting heat exchanger replaced for $750, quote for new carrier was $1750

But carrier isn`t the only furnace company out there. Get several guestimates from other dealers

Do not replace that heat exchanger,it's a waste of money and you are investing in something that will need to be replaced in a couple of years. Carrier is going to be one of the more expensive furnaces, get some estimates from a couple of different contractors.

I don't know of any residential company that will even suggest that you replace the heat exchanger.

Go to furnaceclaims.com, as part of a class-action settlement against Carrier Corp. you are eligible for an enhanced warranty replacement if the secondary heat exchanger fails. Coverage provides for secondary replacement plus 4 hours dealer street labor. I've already lost count of how many I've changed like this, but I typically spend 1 to 1 1/2 hours and the unit runs like new. In most every case, no cost to the homeowner.