HVAC system quote too glorious? I just received a quote from a reputable company here within so...

I just received a quote from a reputable company here within so calif for my hvac system in my 1500 sq ft house. System is a 13 seer 3.5 ton ac and furnace replacement. Quote is $6000 including rates, installation, new vent covers and a washable filter. Seems valid to me but my neighbor thinks its too elevated. Sound reasonable? They be limited by the space they have to work with for both the outside and inside element.
What is the do of diagonal cracks within...
Answers:    I have be amazed at how much heat/air units own increased in price over olden times 18 months. I was buying fresh 3-ton split systems for $1600 in 2005 and today they are more than $2,200. I'd read out $6,000 is about right. Get another estimate from a reputable company to make somebody`s day your self. Make sure the estimates are for the same work - you can't compare apples and oranges.
Why is sand put on modern asphalt?
Ask your neighbor if he's an expert. Sounds in the order of right to me too!