Depends on the company that quotes you, does the work, etc...
About 4 months ago, the coil portion of the downstairs A/C in our house failed, and we lost all cold air. Because the original unit was 10+ years old, and new units used better tech, etc.. we decided to have the entire downstairs system replaced.
The company that came out diagnose the issue tried to quote me $9,000 for a 2.5-ton, 14-Seer system, including the outside compressor/heat exchanger, upstairs coil, blower, installation, etc..
I went online and found a range of prices, down as low as about $4500 installed.. Ended up going through Home Depot, paying abot $5800, and because I went through HD, getting 0% financing for 3 years. Also, the unit that was installed through HD is a Lennox unit, which we know is a good brand. Home Depot contracted out the work to a company called 'Chas Roberts', who has a great reputation, and as it turns out, installed the original A/C in the home as part of the new build.
You can bet that the company who wanted to charge me $9,000 (for a cheaper-brand unit, I should add), was including MASSIVE mark-up on the install. They also wouldn't finance for under 9.9% interest.
Call Home Depot - you'll be surprised.
Oh.. and one other thing - Because the Lennox unit that was installed by Chas Roberts/Home Depot has a 3-year "bumper to bumper" warranty, they threw in 3 annual system check-ups for free because that reduces the chances it will break during the warranty. IMHO, this also helps reduce the odds it will break just out of warranty too!