if you are usa, go to autoeurope.com to see locations and rates. as i recall, the 3 day rate and the 5 day rate are similar.
it is not that big a deal to get out of florence with a rental car as it is to get back in(impossible). and park (whatever the word is for even more impossibiler).
the people at the rental car agency will probably give you wrong directions, but just keep going southwest, and you will be out of there.
it is very hard to avoid a stick shift diesel.