docteur, profit margin on construction is a lot more than 10-15%. In Texas builders sell 1500+ sf houses for $150k. including the land and still make a healthy profit. The cost of material should be the same everywhere. Labor in California is only slightly more.
I wanted to build a 3-wall 300sf addition to my house and the contractor wanted $100k. For that price, I’d rather go to school and find out how be be my own contractor. Builders would like us to think that it cost $200/sf to build a house. $80 to $100 is more like it.
Builders make a lot of money. If they overpaid for the land, well too bad.