The engine is basically a collection of life limited parts, so the range of value in the engines depends hugely on how many engine hours flown since the engine

The engine is basically a collection of life limited parts, so the range of value in the engines depends hugely on how many engine hours flown since the engine was last rebuilt. They can be worth a few million dollars removed from an aircraft that's otherwise unsaleable (to swap onto the remaining aircraft still in service) or of negligble value themselves.