There are many, many hotels in DC, most of which are only a short walk, cab ride or Metro ride from Kaiser's Public Affairs Center. The following is a short list of the closet hotels, though probably not the least expensive:

The Marriott at Metro Center
775 12th Street NW
Washington, DC 20005
(202) 737-2200
link

There's also the JW Marriott
1331 Pennsylvania Avenue NW
Washington, DC 20004
(202) 393-2000
link

the closest hotels

$200+

Comfort Inn, Downtown DC
1201 13th Street NW
Washington DC 20005
(202) 682-5300
link

Recently renovated. More affordable, though location is not as convenient as others.

$137+

Hotel Washington
Pennsylvania Ave at 15th Street NW
Washington, DC
(202) 638-5900
http://www.hotelwashington.com

A classic DC hotel

$200+

George Washington University Inn
824 New Hampshire Avenue, NW
Washington, D.C. 20037
1-800-426-4455
(202) 337-6620
www.gwuinn.com

Very near GWU metro stop on orange/yellow line. Amenities include high-speed internet access in all rooms, valet parking.
[online reviews and info]

$179 +

Hostelling International, Washington, DC
1009 11th Street, NW
Washington, DC 20001
link

A youth hostel at 11th and K NW. Within walking distance of Kaiser.

$29-$43

Allen Lee Hotel
2224 F St NW
Washington, DC 20037
1-800-462-0186
(202) 331-1224
www.allenleehotel.com

A youth hostel only a couple of blocks from GWU campus. Near GWU metro stop.
[online info]

$45-$58