www.elitefourum.com/t/mitsuhiro-arita-experience-milan-cartoomics-march-3-5-2017/15861/1
We charged 2.5€ per signature for the ones present at the comicon, I think 5-10€ per card for the via mail service.
You could have max 20 cards signed iirc, but you could do another 3hours queue to get other cards signed.
Read the article for sketch prices.
He will come back to Italy one day soon, I will make a thread on here when will be that day.