Normally a person wanting to purchase this type property would have many counselors to provide financial information of this,as to h ow to take title, the amount of down payment, if stocks and bonds would or could be used as collateral.
Most individuals purchasing a house in this price range would not really put anything down on the property, they would work out a deal with the lender as to the necessary transfer of other financial instruments that would equal the down payment to the lenders financial institution. This collateral might be stocks/bonds or precious metals or some type of government financial instruments.
Normally the same as the purchase of a regular down payment would be required. This is approximately 20%, the rules of th down payment do not change because the price of the property. change.
I hope this has been of some benefit to you, good luck.