I tend to go by a modified zone dollar amount. That's sort of like saying that to do the work you're going to charge a base price, and then adjust it.
You may want to figure out something like $$$ for installing one drip zone, then modify that up or down depending upon expense and how difficult the zone is. For example, if you have to run wires or a line under a sidewalk, run several laterals or an extra long length, or install a module in a controller, then you would want to bump up the price a bit. But on the other hand, you could give the client a break for a very simple, short, and straightforward zone, such as one where an extra pair of controller wires happen to be right where you'll be installing the valve, etc.
