They are pre-pay non-refundable, but they are there as of 11:10PM. so you are looking at $2000 for four days.
I decided to check for our favorite hotel for no reason, and was surprised to find rooms. No other downtown Marriott has any, but Westin.
Good luck and happy hunting.
Westin, Alexander, Hyatt and a couple others usually keep a couple out of the housing block. But they charge almost triple price for the rooms.
There are some hotels not in the housing block if you look, though be careful, there are reasons they are not in the block.