It sounds like the Cannondale is a "six13 r2000" model, which, in my opinion, is a bit much for a bike equiped with Centaur.
And, if that Giant is the one with Ultegra, Shimano wheels, and an aluminium steerer on the fork (which you can't see looking at the bike), then $4,500 is way too much. The 2004 models are now selling for $3000, and less.