If you find free lodging, then not that much. Food is in every range, you can cook and sometimes eat on the street, and you'd probably average €30 per day. If you want to take on activities, that's extra. You can also spend a fortune on nice hotels and restaurants. Italy is really beautifull!!!
How much you spend there...What sort of accomodations and food you use. How many souvenirs and what types you buy.
If you can walk over the border, stay in a campsite, and eat bread and water, bring home only post cards as souvenirs, it's going to cost you a lot less than if you have to fly from a small airport in California, stay in the Ritz, eat and drink expensive foods, and buy fine leather, cars, gold jewelry, fancy fashions as souvenirs.