Do you have a Marriott branded CC yet? If not, you could sign-up for the base Marriott Signature Visa. It comes with a Cat. 1-4 free night cert, 20K bonus points and the first year there is no annual fee. (You can cancel the card before the first year if you don't want to pay the fee.) If you want a Cat. 1-5 free night cert each year there after, sign up for the Premier Marriott Visa. It has a $65/yr annual fee, but that free night at even a Cat. 5 hotel more than makes up for the fee.

If you have 52K points, you could stay 4 nights at the Arlington/Crystal City CY (Cat. 3 property.) I do believe the website says that they have a complementary shuttle to/from the Metro. But if you can get a Visa card, that extra night and points would allow you to spend 5 nights at the Cat. 4 Cyrstal Gateway Marriott. Now, as a Gold, you will get free breakfast in the mornings and snacks in the evenings. That can help you save even more money. If you stay at the Crystal Gateway Marriott, there is no need for a shuttle to the Metro as the hotel is right next to it.

If you already have a Marriott CC, does your wife? If not, she could apply and get the cert and the bonus points. Marriott does allow spouses to combine points for awards (actually based on posts here, Marriott doesn't even enforce the "spouse" rule. So you could combine your points with just about anyone.) So you could still make use of her points along with yours.