My question to you is: "Why don't you do it yourself?"
You sound like you have some knoweledge about HVAC...Maybe?
Not to take away from anything you've said, BUT, my take on this would be to:
1) Call a reputable company
2) Tell them what you want to do
3) Leave out the useless information that the sales guy doens't need to know
4) Supervise the installation...this may cost you more.
I would hope you would get more than one estimate on this job. Pick someone who will work with you, if it doesn't go how you want it, then bring up everything you know!!