Too bad--I just bought a cyclo cross, Bianchi Axis, after trying to find a used one!! Maybe yours was the wrong size anyway. But to the point, I sold a road bike on Road Bike Review, and found it to be an easy, efficient process, and only a few dollars to list. They have a section for cyclocross bikes specifically.

My son packed the bike in a used bike box from a LBS for shipping, and I shipped it at a reasonable rate thru Fed Ex Ground (about $30 I believe) from Maine to California.