Have fun in Italy!
Italian brands are usually cheaper in Italy, but usually not significantly so, and it depends on many things including the exchange rate and the fee charged by your credit card company. Unlike in the US, the prices quoted in stores already include the sales tax, so you don't have to add anything. Sometimes, you can recoup part of the sales tax (not sure how much) if the stores gives you a form that you need to stamp at the airport; however, not all stores do so and if they do, they do to large purchases only (more than a couple of hundred euros). So I would not consider the tax reimbursement when deciding whether to make a purchase, though of course if this happens much for the better.
If you look around, there are a few threads on this forum on stores to visit in Italy and stuff to buy. Among the cheap brands, you might want to consider l'Erbolario as well, which is quite inexpensive in Italy.