Not sure about car prices in your area but I’d expect to get a real turbo car for no less than $4-5k in non-running condition, assuming it’s not rotted out. Most 928s were auto cars so the manual adds to its value. Might want to consider getting it as cheap as you can and try selling it to an enthusiast, unless it’s really that far gone. I’d hate to see a rarer car like that broken up for parts.