Not the closest hostel from station, but a great price and a nice room (ours had a sweet balcony). You can walk there from RW station (15min) but there are also buses very often. Close to nice restaurants, supermarkets and to some landmarks (Nowy Swiat Avenue, Lazienki Park, palace of Culture and Science...).
Reception open 24/7 but doesn't provide breakfast. Staff friendly and lots of maps/information about the city at your disposal.