As Neil says part complete models which this one would be tend to be are worth 50-60% of the cost to buy a kit. This does vary a lot depending on workmanship and general condition of the model and another big factor is whether the castings are still available. This is a plus in some ways as if a part is missing or needs to be remade then the new owner should be able to get them, if the castings are no longer available then rare and desirable kits can fetch a premium from collectors.
Cost of your fathers Nemett which looks complete will depend on if you can show a buyer that it ran, which unless your Dad took video would be hard for you to show.
J