The answer to 'cost of heat exchanger' is that the cost can vary widely depending on several factors. As an HVAC expert, the main things that influence the price of a heat exchanger replacement include the size and type of unit, the complexity of the installation, and your local market rates.
In general, you can expect to pay anywhere from $800 to $2,500 or more for a new heat exchanger. Larger, more complex systems in older homes may be on the higher end of that range. It's important to get quotes from several local HVAC contractors to understand the typical costs in your area.