QQQ sez:
<< So if the work will be in an attic without a finished floor (where someone could fall through the ceiling), therefore requiring one of your more skilled installers, I think it’s reasonable to charge more for that. >>

What am I missing here? If it does not have a finished floor, it is an attic; if it has a finished floor, it is another story! The work in an "attic" with a finished floor almost MUST cost more, especially if it involves running wires to locations where speakers are to be mounted in the ceiling (of the room below.) The wires need to be hidden, holes cut in the "floor...."

We can't charge more for a person to work in an unfinished attic than in a crawl space just because, to look at the issue of the unfinished floor, he has to keep from falling through the ceiling but does not have to worry about floating up between the floor joists when he is in the crawl space!

Let's say i am in the attic of a two-story house and I crawl out over the foyer, where the drop would be twenty feet instead of 10. The rate does not go up. This actually happened, and it was all the more surprising because I was actually walking on the ceiling joists, and there was only insulation, no drywall, on the ceiling below me. A piece of insulaton fell out and i was looking down 20 feet. Made me glad I walk attics carefully!