Question on replacing ac unit in duplex in my first property

[Cindy Joseph]

Hello everyone, this is my first investment property and home. I am looking to replace an AC unit in a duplex I have in Brevard county,  Florida. HVAC system already in place but the ac units are not functioning. I was quoted 9k for both side- wondering if this is a fair price. 

Each unit is about 800 square feet. Would a 1.5 or 2.0 ton be more appropriate.