Assuming a 4% interest rate and 30 year mortgage that 700k house will also cost you $500k in interest and therefore the financing cost of that house is $1.2 million. The fun part: dropping interest to 0% raises the price of the house to $1.2 million without raising the financing cost.

What dropping interest rates does is not prop up the price of housing, it's increasing the resale value of the housing you already pay for.