Ken, I can assure you, I've made some bigger boo boos than adding
You want to see a prostitutes market in HVAC new construction? Come to N.C. That said, you couldn't pay me to move into these 75-200k cookie cutter homes. The big national home builders build them as cheap as possible and will take price over quality no questions asked.
The prices I got was in the $15,000 range for a 3 ton unit. Unbelievable.
I'd say you're probably right, that is unbelievable for a simple retrofit with a quote from mutlitple contractors.
Some questions
1. Retrofit or new instal?
2. If new install, do you need a duct system installed?
3. If new duct system, is the duct metal or fiberglass?
4. If new duct system, any major construction to the house to fit ductwork in?
5. If metal duct, is it round or rectangular, and is it lined or wraped?
6. R-value of the duct system?
7. Zoned system?
8. Seer/EER/HSPF rating of system?
9. Variable speed or non variable speed?
Bottom line, you need to know what you're paying for.
That said, couple years ago I did a changeout in my attic. Due to the lineset length, I had to change the location of my outdoor unit and re run a new lineset. No way I could do the job by myself with the position of the indoor unit and coil (we're talking PITA). With the help with four other guys, took a total of 56 labor hours in two full days. Again, that was retrofit only job that only required a new supply and return box be built, along with some dampers that we placed in the existing ductwork to balance the air flow. That was a new 13 SEER heat pump with an 80% variable speed two stage gas furnace with a Honeywell T-8000 t-stat with outdoor sensor. When that job went it, it could of been quoted for over 10k no problem. By chance if I wanted to replace all the exisiting ductwork in that attic, over 15k no problem. Keep in mind, that was a couple of years ago. Metal, copper and equipment have all gone up in price since then. Point being, depending on what you're getting for a 15k quote, it may not be unreasonable.
All that said, don't think I've giving any secrets out that in my neck of the woods, for a simple 3 ton retrofit job, you'd be looking at between 4k-7k depending on the type of equipment, quality of workmanship (and there is a difference that when doing an install the homeowner would never know about, like taking the time to pull a vacuum on the system under 500 microns or the type of solder the company uses when brazing copper joints which will ensure that the system will run properly for years to come) and overhead of the company you're dealing with (yes, a one man show can do a job cheaper than a company who employs more people than you can count on your hand not including office staff).
Heck, worse case scenerio, call a contractor who sells Goodman. They're usually the cheapest price in town
Sometimes you do get what you pay for, sometimes you don't.