I went into Expedia to see what's available those days, and Sixt was ridiculously priced. I never liked dealing with them even at normal rental prices anyway.
Budget Car rental is more like $253 for manual shift mid size cars, and the same car with an automatic is more like $292.
There are other car rental options available online.
Beware that the government in Italy requires DPW insurance to be purchased on all rental cars. And the DPW fees should be reasonable by government mandated rates. But rental companies often throw personal goods insurance on the rentals that pays if your personal belongings get stolen--a rip off. This is optional and can be declined. Also note that anytime you rent a car at an airport or train station, they will charge a "location surcharge" that can be avoided if you rent from a city center location.
There is a radar-camera on the causeway out to Venice that issues tickets to drivers going 1 kph over the posted speed limit of 35 mph equivalent. Don't ask me how I know how to pay tickets to city checking accounts in Euros from the U.S.