You can get a free cat. 1 night with 7500 points (6000, I think, if you can find a point saver rate on it). To get to that balance, you can rent cars with Hertz using your MR # for credit (500 points per rental regardless of length), or make purchases with the Marriott Mall. AFAIK, MR points don't expire, so you can take your time adding more to your balance.