While costs have risen, it's not reasonable to compare a kit-house like the ones Sears offered, to a house built on-site.

Looking for kit-houses, I found: https://rethority.com/kit-homes/

Where it says "On average, expect to spend between $40 to $60 per square foot to complete your kit home build."

So that's right in the ballpark of the above inflation-adjusted cost of $45/sqft a century ago.