Why so expensive? Anyone ever use 50+ year old old growth lumber to build a new house with? What are your thoughts on it. Would you do it again?

I'm not sure it would meet code in some areas. Generally, lumber has to be grade-stamped, although I don't know how many inspectors pay attention to that. Used lumber is, well, used, so no one knows what stresses it has been subjected to over the years, not to mention rot and insect damage. I used reclaimed wood for my flooring, and there were lots of pieces that weren't structurally sound. Reclaimed wood is expensive because 'harvesting' it is labor intensive, and it is used in cosmetic applications for the 'look'.

That makes sense. I remember back in the day I worked for a demolition crew. We'd take a house apart piece by piece and we charged for that. I know it was getting used again. Just didn't realize it'd be so pricey.