Seat-of-the-pants "analysis": Dura Ace is Shimano's top-of-the-line. Off the top of my head, I see bikes with components two "notches" lower (Shimano 105) for $500-750 or more. A LOT depends on age (vintage/technology) and condition of the frame, components, etc. Cannondales are aluminum; have the frame checked carefully for cracks. If it's in reasonably good shape, it's a tremendously good deal. Even if the frame is cracked, a good Dura Ace gruppo is worth at least that.