Biltmore House [1], the largest private home in the United States, cost $5,000,000 to build in 1895-1900 (I think it's a beautiful home and I would love to have it's library). Adjusted for inflation, it would cost around $160,000,000 [2] (maybe more, depending upon how you figure inflation). In fact, I'm not sure you could build that today for any amount of money.

[1] https://www.biltmore.com/

[2] https://www.measuringworth.com/calculators/uscompare/result....