Well, I'm not sure about what people charge in your area, but it sounds high. I just put in a heat pump system for my aunt, who lives in Indianapolis, and I was $2000 cheaper than the local dealer and I made *decent* money, for a family member. Heres what I would do: First off, I like Trane products, although Carrier is a good brand. Thats just a matter of personal preference. Tempstar is a "generic" brand, not too bad, but not on par with trane or carrier. It is the same as a comfortmaker, heil, arcoaire, kenmore, and maybe a couple other brands. The worst place to go for heating/ cooling is SEARS. They are 100% higher than anyone else, and I'm not kidding. I do the installations for them, I know what they charge, and they tell me to double my price to give a customer an estimate. And they get better deals than I do on stuff!
I need to know what else you're getting with this. Do you currently have a system, and are just replacing the main components, or are you adding central air from scratch?
Call a Trane COMFORT SPECIALIST DEALER. Not just a trane dealer. The comfort specialist dealers must maintain a very high customer satisfaction rating to have the title. For what you are getting, assuming you already have the ductwork and are just replacing the main components, I would get the variable speed air handler, 13 or 14 seer, and either a 5" media filter or electronic air cleaner. You need to think of what you really need. Do you have allergies? Is there a need for good air quality in your home? If no, forget the big air cleaner thing, it might not help you. A 1" filter is fine for the equipment. The big high effienciency filters are only for you, not the units. The variable speed is good for houses that have noticeable temp differences from room to room, like 2 story houses, bi levels, etc. If this is not a concern, then get a regular air handler, and save the money. I do like the 10 year parts and labor warranty, as the newer high efficiency units can be very pricey to repair. Sometimes 1 bill can cover the cost of the warranty.
It sounds like to me the prices you have now are approx. $1000 high. If you call a Trane dealer, you can tell them your friend has a dealership, so they will realize you have access to pricing, which may keep the price down. Its important to go with a reputable established company, because when that system breaks, and it will, you need to be able to get ahold of that company to fix it fast. Get lots of estimates, shop around. Let me know if you need more advice.