With a central air conditioning system, you get what you pay for. You have to be careful in term of the quality and efficientcy of the machine. I went with a very high end machine in my latest house, but previously I found the Trane system from Home Depot was pretty good for the money. If you're looking for someone honest and who does amazing work I would recommend Layton at PML heating, his number is 613-821-9714. He's usually pretty busy, but he'll tell you honestly if he has the time to do you're job.