Is $18,000 to install a Weil-McLain GV90+6 boiler with NTI indirect water heater a fair price?

My chimney is not lined, and my 30+ year old Dunkirk natural gas boiler is inefficient. My 40-gallon direct fired water heater is also 15+ years old. I want to replace both to avoid the cost of lining the chimney and to upgrade my HVAC. I plan to repair the brick chimney but not line it. I prefer to stick with cast iron boilers due to their reliability and the great radiator heat, avoiding combi/mod-cons if possible, but I am open to other options. My 100+ year old house has poor insulation but reliable radiators. I'm looking for a simple, reliable, and dependable system with low maintenance. I am getting some other quotes.