I guess I would just enjoy Tuscany two days longer and fly - from Florence to Frankfurt, or if that

My family of 4 will be traveling from Florence to Frankfurt in July. We planned to rent a car and drive with a one night stay in Lucerne. Unfortunately the fee for dropping florence italy hotels the car in another country is almost $1000! florence italy hotels We have checked several rental agencies including Europcar.
i think that part of your problem is that your starting and ending countries are not adjacent. when we arranged florence italy hotels to rent a car at Geneva florence italy hotels airport and return it at amsterdam, we were charged quite a high drop off fee [not $1000, though as we wouldn't have paid it]. When we got to the hire desk, they upgraded us to a much bigger GERMAN car as it was better florence italy hotels for them to do that, than for us to have the smaller SWISS one we'd rented - because the german car would be a lot easier florence italy hotels to return to its base from Holland.
Driving is not the best option anyway if you just have one night. If you wanted to explore Switzerland or the Alps for a few days it would have been a nice idea. But this way it will be just 2 days on the freeway, a couple tunnels, a LOT of money for Italian and Swiss motorway tolls and gas ( you can check both if you use viamichelin.com to calculate your route) and a few hours at daylight in Luzern. You will be driving in peak holiday season so most motorways should be packed - though more north-south than south-north to be fair.
I guess I would just enjoy Tuscany two days longer and fly - from Florence to Frankfurt, or if that is too expensive, low-cost from nearby Pisa to Hahn, which is a 1.5 shuttle bus ride from Frankfurt. But still more comfortable and less expensive than the other options.