Your area makes a huge difference in new home construction costs.
Locally one area has ~$20k in 'impact fees' and another $20k in plan review and permitting. Some states water will cost you dearly (If it is even available). Some places are nearly $200/yd for concrete, others are still $70 or less.
I have built several, as well as each of my kids had to build a place from scratch as a homeschool project. All were rural, on acreage, in a federally protected 'scenic' area (lots of 'permit hoops to jump thru). We did our own septic systems (Design and construction), as well as home design & construction.
We usually build ourselves for ~ $40-$50/sq ft, with solid wood trim & Cabinets/ linoleum / carpet / fireplace / energy rated insulation (including site development --i.e. road, clearing, well, septic, power) / . Being your own general you can do the same for ~$70-80/ sf and get done a lot faster... (We did one 4,000 SF with complicated design and steep lot; start to finish in 4 months). To hire out the whole job, $100 - $125 / sf in a normal market. $200 in 'upscale'
I prefer to buy a trashed mobile on a good parcel, with a view & decent well, and BE SURE it has a legal placement permit ! Then trash or replace the mobile. Or, for tax reasons, build a dumpy shop with a really nice apartment INSIDE away from the view of assessor. My neighbor has a 'killer' apartment in a 120x200' shop. Really nice / Marble / Stainless / fireplace / loft / deck with mtn view. ... looks like a warehouse from the street. His taxes are $1400 / yr
. Mine are $12,000
He has room for a couple semis, car hoists, and indoor motorcycle track (stadium Trials). My bulldozer has to live outside