I don't think the cost of labor is as much of a factor as options wanted by the customer. In comparing several smiths before having my 2011 built, they were all about the same ballpark. The primary difference between them was timeline.
The difference between a custom 2011 running $2.5k and $4k could be the difference between using mostly STI parts and WC bulletproof parts. Aesthetics such as FCS, serrated flat top, French border and finish just to name a few.
Keep in mind, smiths doing full builds aren't getting rich. It's more profitable for them to spend an afternoon completing trigger jobs and flush cut barrel crowns and it is to spend a week+ on a single build.