If the Bianchi is in good condition and the components not badly worn, that's not a bad price for a 105 equipped bike.
Buying a much older bike and upgrading it can be a tremendous money pit even if the bike itself in nearly free. There is alway the question of parts compatibility such as rear dropout spacing and steerer diameter if the bike is old enough and buying individual components is much more expensive than buying a complete group on a bike. It can be done by knowledgeable buyers with patients and a good understanding of what they need but I don't recommend it for a new owner.