A basic menu with just buttons and links should not take more than an hour if all the artwork is provided as well as accurate requirements definition up front. Considering a usual lack of the well-defined requirements and back and forth I would go two hours for an estimate.
Any estimate needs to be predicated on your understanding of the scope and the client's understanding that a change in that scope means a change in the effort/time/cost. So if the client was answer back to say the number of buttons is quite large but they still won't say how many, I would just say that I charge by the hour.
