FISHER 500c what's it worth?

My Dad has one of these. He is the original owner. I know firsthand - I used it for many year during the 80s. It is in good shape, has the wood cabinet. The only issue I am aware of is that the volume knob does not turn the power off. I used a cord with an inline switch to turn it off. Other than that some of the output tubes were replaced by me. Sylvanias I think.

I realize it probably needs to be restored with new caps, etc.
Any clue to what it is worth? Thanks for any help, and if someone is interested let me know. It will be posted soon.
Thanks!!!