Are there any easy paid parking lots outside the city walls?
There are many on the viale or ring road around Florence (look for a dark blue sign with the big white "P" on it - and/or electronic signs which show digital numbers with the amount of spots (posti) let open) - you are usually pretty safe approaching Florence as far as the ZTLs, etc. except if you are coming from the south where there are still a couple of confusing spots. This site is in Italian but it may be a help: http://www.firenzeparcheggi.it/ This is better with the map: http://www.firenzeparcheggi.it/index.php?id=99