When buying a gift, do not buy a product that is inferior to what the person recieving the gift already owns. Otherwise it probably won't get used much. If your father already has a bike that has a 105 drivetrain, then that is what you should get. If he has Sora, then you can get Sora or 105. If he has Ultegra or Dura Ace on his current bike, then you might want to upgrade to either of them.
If he has no bike or one that is very old and just want to get back into riding, then Sora is fine. If he is used to riding well maintained 105 or above, Sora is going to be a big enough step down that it will be noticable once the the components start to break in.
If your father is a die-hard Bianchi fan like I am, then he probably would prefer the Bianchi Celeste color rather than the black. Any Bianchi that is any other color than celeste is a "fake" Bianchi.
Why dont you just get him a gift card for the full amount you are willing to spend from the local Bianchi dealer. Other family members may be able to pony up a few bucks for gift cards also. Combined your father may be able to get The "Infinito" in Celeste with 105 or better components. If he loves Bianchi I am willing to bet that this is the bike that would bring him the most pleasure. As KD has stated the Celeste color announces to the world that this is a true "Bianchi".
