Furnace Heat Exchanger Replacement

I have a Ruud 90+ propane converted furnace 105000 BTU that was installed in 1996. An A coil was also installed above the heat exchanger. as part of an add-on AC system. The refrigerant is R22 and the system was added in 2000. Both systems are working extremely very well. I have done minor work myself on the system ( replace inducer blower, igniters, cleaning the burner ports, new gas valve, gas pressure check, cleaning the AC coils & condensate drains, replacing furnace filters regularly). I have CO monitors and check the heat exchanger for leaks each season. I don't run the AC much (maybe 2-3 weeks per year) since I live at a high elevation in the Pocono mountains. I want to purchase and install a replacement heat exchanger Ruud/Rheem AS61805-20 cost about $3000 if I can find one. The other alternative is a new furnace and AC system (unless I can pump down the R22 into the condenser unit and have only the A coil replaced). I could also go with a heat pump propane backup. How would you technicians approach this? Would you replace everything or replace the exchanger?