I really did a great job budgeting my trip to Italy the following ways:
1) I planned everyday and bought my tickets ahead of time via TrenItalia. That way I stuck to my schedule, but when I bought my tickets, also provided myself with some flexibility in when I returned, etc. Buying tickets in advance actually proved to be cheaper than abroad. A round trip ticket to Naples was 9 euros pre-trip but out of curiosity I looked at the prices at the station the day of and they were significantly higher.
2) I looked up prices for places I wanted to see and set that money aside for each day. Each day had it's own envelope with money including some spending money for fun. it also included meal cash. While this seems like it'd be a bit frugal, I made sure to make sure my daily amount was fairly generous and I often had cash left over. I always took my card with me, just in case. I also liked having money in it's own envelope because it's not obvious what is in it, so if a pickpocket got into your purse it wouldn't be obvious it's money, so they'd be less inclined to steal it. (Yes, I had an incident in Pisa) and it also keeps you from spending past your means. Always always keep a separate stash for emergencies.