Much like the story of the Team Track above, I ride a 2011 Trek T1. I put bullhorns on it and changed my seat (not looking to drop weight at all) and it weighs about 16.8lbs. I bought it new and complete for $600 (w/o tax).
Throw on some carbon components, maybe change the wheelset, and there you have it. A sub 15lb bike.
The District is just a Madone with different dropouts..and I have a sweet spot for Madones, so just buy the district and post some pics!
.Chris