What would it cost be to buy down the interest rate from 4% to 0 on a $500,000 home price?

More than likely, more than you can afford or are willing to pay. All investors have a floor that they will not allow the rate to be bought below. Today for my pool of investors, the lowest rate you could buy down to is 3.25% for a 30 year loan. That would cost you 1.5 points. ~ Bert Carpenter, The LoansA2z Team of NOVA Home Loans. NMLS 40586 ~ 888-889-9950

Not that I know a bank that would go for it, but in a hypothetical world, I'd estimate about 7 years worth of interest.$500,000 x .04 x 7 = $140,0007 years seems to be the break even to recover the cost of paying a point by having reduced monthly payments over that many years.

Zero percent is not even on a rate sheet...buying a point sounds more realistic to 3%