I find it useful to negotiate based on my time, including setup, takedown, travel if excessive. That's what other professional consultants and service providers do. You need not confuse your clients with this unless they ask, but mentally just figure that a three hour gig is really a four hour gig - which it really is. This becomes an issue only if you want to negotiate for more consecutive nights... when my clients want a price break I tell them that I give breaks when I don't have to setup or takedown my equipment - that gets me extra nights, sometimes bumping my competitors out of their nights. Such fun!