Scott,
I don't think the word "not" belongs in the second sentence of your post, other than that I think you are right on with the answers. As far as the cost goes, I think that conduit and wire would be about 15 to 20% more than the SE cable.
If I was the inspector (given that this ins an existing installation and there is no way to force the owner to bring it into compliance with the code) I would allow the installation of a forth conductor run with the SE cable, as long as it is not in an area subjected to physical damage. Even though this is a code violation, it would be better than what is there now.
Don(resqcapt19)
