A $150k loan in 1999 at 7.6% would cost you $1,059/mo in mortgage payment. A $300k loan at 4% today will cost you $1,432/mo - a 35% increase over the original price, not the 100% you'd expect. Meanwhile, you aren't paying 2x per square foot - you're getting roughly twice as much house as you did before for that price, for only a 35% increase in payment!
[1] This is a smallish dataset, but the trend holds outside of the pre-2008 runup. I don't have that data immediately on hand, though. https://www.clevelandfed.org/newsroom-and-events/publication...