Clogged Hot Water System Heat Exchanger

When we fired up the boiler this fall it was blowing the exhaust gasses out into the room (basement) and was setting off the carbon monoxide detector on the second floor. Since this was a "home warranty" situation we just moved in in April, I had to call the warranty co. and got one of their contractors to come out (a plumbing contractor that is licensed for boiler work). $85 later he says the heat exchanger is hopelessly clogged and not worth cleaning and recommends a new unit (which the home warranty will not cover since it is a maintenance problem and not a break down). He said I was looking at something like $3 - 4,000.

I looked into the top of the unit while it was running and you really can't see down into it for all the gunk on the exchanger. You can barely see the fire down in there. It is very clogged as he said. But, I don't buy that it can't be cleaned. The unit is pretty old and may date to when the house was built (1947?), the burner unit was supposedly replaced within the last 5 - 8 years.

Anyone with some experience like to comment??? What would be a reasonable price to have it cleaned or is it something I can do? Anything down in there I could mess up? I know it will need replaced soon but didn't want to have to do it this year as we just spend a small fortune on other things for the place (it's a small farm). I do have another contractor coming out to look at it early this week, the one that put in our A/C and ductwork. Thanks for any advice!

Bill OH