For comparison, I'm a mechanic at a GM (Saturn) dealership. The store charges $89 an hour for repair work. Our maintenance labor rate is less to keep competitive. I think it's around $52 an hour, but not sure.
I can say for certain that good gunsmiths do much more crafting, artistry and specialty operations than I or anybody in my shop do on any kind of regular basis.
And out of that $89 or $52, what does the employee actually doing the work see? About a third? I'm not sure that would be the comparison I would want to make. The high (even overly high) prices dealerships charge just open up a whole new market for independent shops. Some are just as good as the dealerships and some, are not.
A better comparison to a really good gunsmith would be a body and paint guy at a dealership. They do a lot of
crafting, artistry and specialty operations along the lines of what a really good gunsmith would do? Usually body shops charge an even lower hourly rate than service at a dealership, so I can assure you a skilled body and paint guy isn't even making anywhere near $75 x 150% per hour. With the number of skilled craft Plumbers, Mechanics, Welders, and others out of work, I think, given the choice, they will bill out below $75/hour. Let's be real, none of use are calling our plumbers and asking them to mod our water pipes. Or are we?
For what the OP is looking for, "nothing fancy, just a simple 1911 with beavertail (and possibly a serrated front strap)", Caspian could be an excellent starting point. Order the frame with the features you want and beavertail prep. Order the slide with the sight cuts and other features you want. Pay Caspian $50 to fit the slide and frame. Find a local smith that is capable of doing the final fitting of a barrel, the sights and the beavertail, get a drop in trigger kit and $1500, seems pretty doable.
Or, a "mil-spec" complete gun for ~$500 might be an alternative starting point that leaves a cool grand for new sight cuts/install ($250), beavertail install ($150), and maybe a new properly fit barrel bushing (~$50) and some trigger work ($100 and up for a drop in, or $200 or more for new parts and tuning).
I guess it all depends on what qualifies as a "custom 1911". Start adding more "artistic" touches and I think the sky is really the limit.