The best way to find out is to call a few contractors who carry different brands of hvac units to come out and give you a free estimate with all your requirement. Price can vary a lot with different brands, functions, ease of installation in your house (labor hours needed). Also you can look in to mini-split units which are much easier for zoning different areas and more energy efficient in general than central units.

Av

There are three parts to a successful new HVAC installation.

1.a quality dealer and install, a dealer who listens to the homeowner's concerns and goals
2.quality HVAC, brands/models are not the same.there are lots of junk in the residential marketplace
3. And probably the most disregarded and overlooked is a quality ductwork system sized correctly both supply and return and insulated and checked for leaks. Any hot/cold spots should be addressed as usually they are ductwork related.

Now to your situation. New HVAC should be sized correctly usually for
average temps both heating cooling, not for extreme temps for your location.

It is difficult to heat and cool two story home off one system. You can control airflow manually to each floor with dampers on the supply lines. Next would be zoning controls. This can be problematic on retrofits. And the most effective would be two separate systems.

You need to know the features you are looking for both cooling and heating such as var speed furnaces, efficiency, sgl stg or two stg condensers. How bout indoor air quality and filters? Don't assume. Read up and be proactive with dealer's that are quoting. Know your warranty.

Just a few ideas.

IMO
Good LUCK!