The pilot was departing from a remote, 800-foot long gravel-covered airstrip, in variable wind conditions. He said that during his southerly takeoff roll, just before liftoff, a gust of wind pushed the airplane to the right. As the airplane became airborne, he felt a "bump" but he noted no control or vibration problems. After an uneventful landing at his destination airport, an inspection revealed substantial damage to the lower portion of the airplane's rudder. The pilot reported that there were no preaccident mechanical anomalies with the airplane.