The only time when a take down rifle looks good, is in its case..... Just my opinion.

To answer your question: the expensive part is to make the front section of the stock fit perfectly and lock into place. Cutting the threads on the barrel to unscrew is the least part of it.

So no, a converted rifle shouldnt be expensive to revert back to a take down.

I have seen 275, 303, 350 Mag and 400/350 take downs, but NEVER a 416. I stand to be corrected and welcome it. If they exist, It must be something!