I just rewired my Mariner 39 to current ABYC standards. It was expensive but after seeing what shape the 20 year old wiring was in and the potential fire hazards I prevented it was worth the cost. I hired a professional marine electrician to do the work. The total cost was $7,200. I went with only the best wiring and panels. The panels alone were $2,300.
Again expensive, but when you consider that most of your problems on a cruising boat are either engine or electrical, the cost was worth the peace of mind I know have.