Depends on who does it and what all they're integrating. Expect about $40 per hour for a good installer. If they're merely cutting boards to fit and carpeting it, that shouldn't take more than a day or two, figure $300-600 on top of the components (I'm guessing totally on the required time, BTW). If you go for a more elegant, more integrated, more "factory" look in which they fiberglass in the components, I was quoted $1600 in work.
I wouldn't opt for anything less than a fully fiber glassed enclosure on a luxury sedan or coupe, personally.
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