I'm guessing getting a Lot in a good zip code, and then having to match housing requirements from local zoning or the HOA is what drives prices. Rival goods basically.
I think one major hangup is finding the labour.
I have almost no construction skill, and also work a full time job. I can't take on a kit house myself without becoming homeless in the process. Any contractors I talk to are so busy they are booked out months (or years) in advance.
Another hangup seems to be the design. Any contractors I have found who are willing to build, only ever want to build/sell you a house they designed. And they all seem to exclusively want to design/build suburban homes on huge empty lots that (in my opinion) look like dated McMansions.
I would love to build a small (900sqft - 1400sqft) modern kit/prefab house on a small urban lot like this: http://farm4.staticflickr.com/3920/14620317361_5766da68c1_z.... or http://prefabcosm.com/media/photos/2008/01/12/ecube1398.jpg
Every home builder I've ever talked to will only (exclusively) build huge (1800sqft - 3000+sqft) homes, on large empty suburban lots, that all look like this: http://www.mayberryhomes.com/CmImageDir/inventory_1695.JPG or https://nhs-dynamic.secure.footprint.net/Images/Homes/AllenE...
https://www.menards.com/main/building-materials/landscaping-...
Has an extra bathroom, an extra 2-car garage. And modern electrical, and plumbing.
It's not pretty at all. But it's $7k cheaper ($40k), safe, and is to-code legal in most places.
https://www.menards.com/main/building-materials/landscaping-...
Has 1.5 extra bathrooms, an extra 2-car garage, and modern electrical and plumbing. Probably a closer match to the style, at roughly that price ($46,600). Also to-code legal in most places.
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Obviously we're never going to get an exact match in materials. In many cases, you wouldn't want to -- a lot of safety standards have improved since then. But "you can buy what $47k got you for quite a bit less" is a reasonably accurate claim.
If anything -- kit houses at the $47k price tag are probably much nicer today than the were back in the day. (more space, more amenities, safer, etc)