Hi again!
It's difficult to give value to an instrument without seeing / hearing / playing it. Based on what you know about the instrument, what type of person are you selling it to? Remember also that the person needs to consider moving the instrument - which is further expense. If the person is a restorer, they will probably want it for the lowest possible price (even free) to put their money into restoring it.
Although cheap instruments are tempting to buy for a beginner, there is greater reward for all involved to buy a reasonable quality of instrument to start out on.
Essentially, if it's really only good for restoration, the price will need to be low (<$100 I'm guessing). If it has a case in good condition with little damage, you may attract some interest from a furniture collector (but again, they have to consider the expense / difficulties of moving it).
Again, if you're not sure of the value and condition, have a technician look at the instrument and ask them to be honest, not nice
Trust this helps.