The value of an item is really just what someone is prepared to pay for it.
The seller is probably hopeful that the car is still out there, and if so, that's not an unreasonable price to pay to have further proof to support and boost the car's value, especially if it is now NOM.
Not judging, but consider how much some correct parts to finish a restoration have sold for recently - $200 for an OE speedometer cable clip, $300 for a brake booster vacuum hose bracket, $400 for a set of valve stem dust caps........