ive been living here in italy for the last 4 years and the cost of food here in comparison to the states is 50/50. for example, going to a restaurant or a cafe, they charge for every little dam thing you touch, not kidding. you get charged for the spot you are seated, for the water you order, for the bread if you want any. in the states instead, you get charged only for the meal, water is free, bread comes with the meal, ecc. so having dinner in two in florence goes from 35 euros (not including wine) and up. i recomendation, do not leave tips, because here its not use to and the service most of the time is that good, be real thankful and leave good tips when the person who attends is kind since its not common.
about the groceries, its extremly expensive in the florence only if you go to a grocery store in the CENTER of florence. if you can get access to a grocery store on the outskirts of the center, you can them at regular prices. for example buying a bottle of milk, in the center youll get it for like 4 to 5 euros, in the outskirts, about 2 euros. it makes a big difference.
hope this helps!