has to so with condition and location. Z cars located in the NE tend to have a LOT of rust, if it was garaged its entire life and not exposed to road salt that would be good.
You have to take a lot of pictures covering every inch of the car. Hot spots are under the battery, under the brake master, under the carpet on the floor boards, the spare tire well, the rear hatch opening lower corners. Fender wells around the struts. under the doors.
Need to know if it has ever been wrecked, need the entire bottom photographs. Best way is to have it on a lift, as long as the person putting it on the lift knows the correct lift point.
The point being unless you can document the car with this level of detail it is IMPOSSIBLE to give you an estimate. Body work to repair rust damage and or frame damage from a wreck is very expensive, and any one thinking of buying it with out though knowledge of all the above will have to assume the worse and make offers with that in mind.
You best bet would be to give a location and see if any members are near you to look it over and give advise on what pictures are needed, and tell you what you need to disclose. Only then should you ask for opinions on value.
There have been some very high prices paid recently but that is by rabid collectors with very particular requirements on not only condition but serial number an model year. Typically very early 240's.