I'll answer in general terms, since I'm not familiar with the price ranges in Florida.
The LLC formation costs $125 (state fee). In addition you'll need a registered agent. Registered agent could be your CPA/EA/bookkeeper/property manager/local friend, or you can pay firms specializing in providing registration and agents services such as NorthWestern or LegalZoom (there are many others). You'll need to pay an annual fee of ~$140 in Florida. If you are using someone to do the formation, they'll charge more (usually the on-line services are cheaper than a local CPA or attorney, by $100-$300).
Bookkeeping will probably be charged by the hour, but some bookkeepers charge flat fees for small accounts. Per hour would be probably in the range of $40-$80.
You'll have to pay taxes - both in Florida (where the property is) and on the Federal level to the IRS. You'll be paying them as a non-Resident individual. Your CPA/EA will charge you anywhere between $150 to $500 for that (if they charge more - run away, unless there's some specific complication that requires extra costs). You will need a ITIN for that, your CPA/EA can help you get one or you can apply yourself.
Be careful with all those people selling cr@p about organizing in Delaware/Wyoming/Nevada (like CQM in his answer). Organizing in a state other than where the properties are located (or off-shore) won't save you a dime, and not only that - it will add to the costs. Because you'll have to pay to the state where you organized (CQM mentioned Wyoming - $50/year), keep registered agent in the state of organization (+$99) and also do all the things I've described above about Florida - as a "Foreign" (out of state) entity, which may mean higher fees. It won't save you any taxes as well, because you pay taxes to the state from which you derive income, which is Florida, either way.
Remember that what you call LLC in Italy may be in fact a "Corporation" as defined in the US, and there's a huge difference. You should probably not put a real-estate property in a Corporation in the US.
You must get a legal advice from a (Florida) lawyer ($0-$500/hr consultation), and a tax advice from a (Florida) CPA/EA ($0-$200/hr consultation). Do not consider anything I write here as a legal or tax advice, because it is not. You need a professional to help you because as an Italian, you don't know how things work exactly and relying on rumours and half-truths that you may find and get over the Internet may end up costing you significantly in damages. Also, talk to a reliable real estate agent and property manager before making any purchases.