It depends on what the job involves, and any fixed number quoted before someone has seen the panel is a guess. The main factors are the scope of the work, how far the wiring has to travel, whether the panel or service has room, what finishes have to be opened and repaired, and the permit and inspection steps. A defined job, such as adding a circuit, is priced against a written scope. Troubleshooting is often priced by time, because the cause is unknown until it is found.