Non-running 6.3's that seem visually similar to yours have sold recently for around 10-15k on the major sites, and privately for even less.
You could easily dump 10-20k in parts into any W109 just to get it running and drivable, not even getting into bodywork and accessories. Just the air suspension alone is around 5-6k to have all the major parts rebuilt, and that's just to have the car stay up, not even getting into the rest of the suspension or steering, so be warned.
The body isn't really any different from any other w109 so if the parts that are actually unique to the 6.3, such as the motor, are shot beyond repair then the value as a parts car is not much greater than a regular w109.