A couple of years ago I did a first floor addition, and replaced both upstairs and downstairs units. Not sure if you're getting both heating and cooling, or just cooling, but I had two complete Rheem 16 SEER heat pump units with 2-speed compressors installed, and some minimal duct work, for a total cost of $10K. Both are split systems. They really work well and are very quiet both inside and outside the house.
Your cost will be increased by the need to run new duct work, which is dependent upon access to locate the main ducts, air returns, and the individual runs. I pay about $150/year for the company to come and clean/service everything to maintain a 10-year service and parts warranty.