Is it cheaper to purchase Euro's in the US or in Italy?
The absolutely cheapest way to obtain currency in Italy is using a debit at an ATMs. Probably save at least 50% over what you would have to pay to exchange either in the US or Italy.
This question is answered in our FAQ section, it's the same thing Frank said. For the details, go to our FAQ, http://www.ricksteves.com/graffiti/helpline/index.cfm/rurl/topic/39869/bfaqs-answers-to-frequently-asked-questionsb.html, and click on 2nd item down.