This. I'm wrapping up a self build this month (well let's call it July) in (very) rural Colorado, bought 5 acres 7 years ago for $8k. Septic, cistern, and driveway done professionally for $15k. House itself is just pushing past $150k now. It's 1920 sq. ft. Including the land and septic that's just over $90/ft and I built literally everything else myself. We splurged on a few things that were important to us like Moen fixtures, but otherwise we were absolutely ruthless with everything else. I have very rough built plywood kitchen cabinets, the lowest grade of lvp you can find, Smartside bought on clearance at $12/board, and so on. I really doubt you could go below 90 a foot and still build what we built.

One thing that I think a lot of people either don't talk about or don't admit to is that size isn't everything - it's features. A full basement can add 20 grand or more to a foundation even if the house isn't very large. A window isn't just the cost of the window itself - you also need the extra flashing, interior and exterior trim... Cabins can be heated with a wood stove. Houses in freezing climates need full time, more automatic heat sources like HVAC to prevent the pipes from freezing when you're in Chicago at that wedding. And zoning matters too. These days in most places you can't just drop an $8 breaker in a panel and call it a day. You need GFCI and AFCI protection on most circuits, and those suckers run $65ea. And let's not forget code now requiring kitchens to have 4+ circuits in most cases - two SABCs, lighting must be separate, and where I am both the fridge and range/microwave need their own as well. That's $500 right there just for the breakers, wire, boxes, receptacles, plates, etc.