If you're wanting Campy, then why would you go cheap with Shimano? Strange.
If you're willing to spend the money for Campy, then go with either Centaur or Chorus...or you could mix the two so you would get the best where it matters, and the rest where it doesn't matter.
So I ran that thought through AI and this is what it came up with"
Crankset (arms + rings) | Centaur | $150–$200 | Slightly heavier but fully compatible with a 12 sp chain if you swap to Chorus 12 sp rings (or run Centaur rings with minimal noise) |
Brake calipers | Centaur | $80–$100 | Rim or mechanical-disc calipers; lever-to-caliper actuation is identical across tiers |
Bottom bracket | Centaur | $20–$30 | Campy BB standards match across groupsets |
Rotors & Pads | Centaur | $10–$20 per wheel | Same mechanical-disc spec |
Pedals, BB tool, cables | Centaur | $0–$20 | Ancillaries you’ll need anyway |
Those dollar amounts listed is what you would save from going with all Chorus, the weight penalty doing that is around 250 grams. Personally I would just go with all Centaur, it's a very good and rugged groupset.
If you decide to go with Shimano I personally would go with 105, nothing higher or lower, it's very well price, extremely durable and reliable, replacement parts are cheap and easy to find. You're not going to save much money at all going with Tiagra, but you'll save a lot by not going with Ultegra while only giving up about 180 grams which is nothing. Plus 105 is easier to upgrade later if you decide to do that, but I don't really see the reason to do that.
Since this bike is a commuter bike there is no need to go with Chorus or Ultegra, those are made for people who wish to do some racing, so stick with something reliable and more affordable.