Try Dan Crookston with Rocky Mountain Air Systems. You can reach him at (801) 255-6800. I have used him on three homes we built ourselves and one townhome I owned similar to your situation where he added the central AC after the fact. My wife and I have known him for almost 30 years, his work is top notch and even when we got competitive bids he was always the lowest bid. Assuming you have a pretty standard forced air heating system, my guess is this would be fairly simple and you probably don't even need to add any new ducts. I don't remember the exact cost when we had it installed in the townhome but it was pretty reasonable.