One just sold last week for $5000. It was narrow body C4 roller (no engine).
http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/503940-f-s-parting-1990-c4-no-engine-5k-have-clear-title.html
Is yours factory wide body? C4 or C2? What's wrong with the engine? My guess would be somwhere $6-7k.
Running examples in poor shape sell for $8000-11000.