This will give you an idea of listing prices. As far as repair/update costs, I am ignorant.
Is my Dynaco Stereo 400 worth repairing for resale?
After all the years, I’m sure it needs a good cleaning and at least all the cans replaced.
Will I even break even?
https://drive.google.com/file/d/10BBbN8Vd2_2sgQAoMI8N5CqnWdhASrbH/view?usp=drivesdk