help booking car rental

I just checked your dates using the Florence Airport as your pick up location and the Orvieto rail station as your drop off. I put both times as 10:00 a.m. There was nothing to indicate that either location was closed. What times are you using?

not 10 am so that may be the problem. Thanks.

That's why I asked what times you put in. It's hard to help without all the information.

You'll pay dearly to pickup a car at any airport in Europe as there are often handling charges and taxes not charged in the city center. Just ask AutoEurope for a pickup at 53 Via del Sansovino in Florence, which is a short taxi ride from the train station. That's a Hertz location. Hertz will give you directions to the south that will avoid any ZTL's. I did the same thing last year, and found dropping the car in Orvieto to be very easy. They don't open until 9:00 a.m. on Saturday, however.
Many shy away from renting cars in other countries, but Tuscany roads are well paved, well marked and easily driven if you can handle a stick shift. You can visit three times as many sites with a rental car vs. by public bus.

Just be sure to figure in the cost of the taxi as well as the time wasted going to another location to get your car. I usually just rent right at the airport unless to savings is substantial. I have rented at the Florence airport a number of times with no problems. I always just go to Priceline and see who is the cheapest, and book with that company. I would never prepay a car rental as the rates change all the time and you can rebook at a lower rate if the rates go down (they often do) or you can just keep the current reservation and not be prepaid in case something happens.

If you use Autoeurope, check also Prices for a pick up at Via Forlanini, 2. It's a Europcar location only 5 min from the airport, but classified as city location, therefore cheaper than an airport pick up.
If you plan to visit Florence first, don't be afraid of picking up in the historical center. The ZTL is a danger only on entry (if you don't know where You are going) but it's no problem exiting the city center. Cameras are located at entry points only and there is no chance of being photographed on exit. The historical center locations for all companies are all in Borgo Ognissanti or via Maso da Finiguerra.

We booked through Hertz. Used our AAA card (using ou AAA card code) and got a 20% discount by prepaying on my husband's American Express Card. The AAA card also made our collision/damage (required in Italy) responsibility 300 Euro and car theft 300 euro. Luckily we didn't have to use it, but it was better then insurance offered without our AAA card. A helpful lady on phone told me about it. We rented in Southern Italy area and dropped of in Sorrento. Don't forget to get your international driver's liscense - $15 at AAA.
You need it if you get stopped for any reason.

You should always check with www.gemut.com before deciding. They are a US based company that guarantees the lowest rates.

Since you are renting a car for 3 weeks, you might check out the European lease program offered through AutoEurope. You basically get a brand new car, fully insured, no extras for probably less than the rental. AutoEurope leases Peugeots and someone else does Renault... there are probably other companies as well.