Having been involved with such labour factors in the past, I found they are erratic at best when applied to welding - the estimates can vary in the extreme based on small changes in assumptions. This approach probably makes sense when making the relatively small step from carbon steel to stainless steel, for example, but titanium and superalloys are a whole different game. For example, titanium welding requires much more effort for shielding gas, specialized equipment, even a work area isolated from the other dirtier work going on. Inspection levels and repair rates also may be different. Personally I would be wary of this approach when stretched so far.
IMO a good source of information would be fab shops who base their factors on actual past experience.
