In reply to EliotStephens: In my experience car hire is noticeably more expensive in Italy than in other parts of (western) Europe - I rent upwards of 6 times a year and have done for the last 4 years or so.
Why? Well my guess is that it is because you are in Italy and there seems to be more loons on the roads
Hiring from agencies is generally cheaper but not so reliable. Picked up a car in Rome once, had skis with me plus stuff for a conference so had ordered a decentish sized car, got a Micra as did my bro with wife & 2 kids, he'd ordered an estate. They had run out of bigger cars. It was far from ideal, we got some money off after complaining but would rather had what we had ordered (and had confirmed). With Avis you would get upgraded rather than downgraded if what you order isn't available.
You get what you pay for I guess.