While the basement had certain pain in the @$$ attributes, in general I prefer a basement over not having one.All your plumbing, electrical, ductwork, etc. is exposed in the basement, which makes it much easier to work on.

This is because replacing one HVAC unit out of four is arguably 25% (less if you include duct work) of the HVAC system as a whole and therefore not material to the HVAC unit of property. 

Is the duct work all rigid?

We came across these zone systems that boast being able to heat and cool a large area, have no duct work, are energy efficient, and are less than $2000. 

But even the best brand that is well installed will fail if you neglect to remove build-up of environmental conditions - allow the compressor to swim in horse manure and the air-handler and duct work to be dirtier then a wood-burning chimney.Most new installations should warranty their labor for 6-12months at least, and therefore most will generally offer to perform first 1-2 PM services for free.So, assuming you don't have a lemon product - which you'll know during the first year anyway - the ongoing preventative maintenance on a good, properly installed central AC system can really be done by you, or anyone working for you:1.

I need a whole system replaced with some duct work.

I assume you just need the units not all the ductwork?

Without changing any duct work etc etc, just changing out furnace and adding ac in my area runs about 5k without any discount.

My favorite is gas heat warm air with duct work that can accommodate central air conditioning.Around here in Pennsylvania there are a lot of old houses, many 100 years old. 

They give you a lot of flexibility (no duct work) and much greater efficiency.