I price per opening.
Every gang is an opening - range & dryer count as 2 each
Every component (such as fireplace, ac disconnect, etc) is an opening - in addition to any dedicated circuit
Every breaker space is an opening - in addition to the price for a circuit
My opening price includes basic materials needed for something standard, like a switch or receptacle - roughly $12.00 for materials covers box, wire, cheap device. Anything over that basic price is rounded up and added on. I add $15 for smoke detector, $20 for can light, etc
Labor is an average across all openings, but I add for extensive install such as high chandelier, ceiling fan, etc.