There’s a builder down here claiming she builds them for 125 a sq ft.
That's pre Covid prices . Mexican subs work cheap , but aren't free. I'd speculate she either doesn't know how to add or is untruthful.
She's probably both stupid and untruthful.
If the price is too good to be true...
Here's what happens when you select a contractor because their price was way lower than everyone else. You will either be left with an unfinished, shitty built house or a LOT of change orders you can't afford.
Then you end up in civil court.