When someone says there building a rifle for $400, I figure they're doing it themselves. Since a good barrel cost you usually over $300. A guy usually can't rebarrel for $400 using a gunsmith.
I've been waiting to see if Reynolds357 would clarify what he meant by the $400 quote.
Generally, I would agree with you. But, there are exceptions.
My last build (~2010), a wildcat even, came in at $397. That included the barrel (purchased by me), reamer, chambering, threading, a custom crown, squaring the action, lapping the lugs, polishing, bluing, custom engraving for the chamber stamp, return of the factory barrel, and more...
...from a gunsmith that was not doing me any favors. He charged me his normal rate for everything but the engraving (threw that in for free).
I cleaned up the factory barrel really well, and managed to get $90 out of it - bringing the build cost down to $307.
But, I will admit, that I chose to use a gunsmith that was 3 hours away. So, I burned 12 hours of my time and 380 miles worth of fuel (~$52) for travel.
That gunsmith saved me some money, though, by being one of the most skilled machinists in the state. He is extremely efficient, knows exactly how to achieve the desired results, and just cuts/builds new tools (and reamers) if he doesn't have what he needs. (He doesn't have to wait around for 3-12 weeks for the tool, like every other gunsmith I've dealt with.)