I would NEVER contract to have ANY substantial work done, for a client or for myself, without getting at least 3 quotes that were comparable in scope and precisely defined the work to be done. It is your call, but how long does it take to open the yellow pages, find the HVAC (heating venting and air conditioning) section and call two of the biggest ads (that aren't sears or a big box)? You could schedule them to come and give you quotes in about 13 minutes. Hey, even if you get a lower price and still want to go with your guy then maybe you could get him to back down on his price a little. I would also want to get other quotes in order to get other, on-site opinions on what might best work for you. If no one else seems to think you need zoning then do you still trust your guy as much after he suggested a zoning system that probably cost $1,500 or more?