Returning to Florence after Siena's Il Palio

My dear fellow travellers,

I'll be travelling with my sister and our parents to Italy in late June and early July and am a little bit stumped about one particular detail in our itinerary. In the middle of our trip we plan to be in Florence for three nights, from either June 30th or July 1st. We'd love to see the Palio horse race in nearby Siena on the 2nd. We were planning to make an all-day trip into Siena on the 2nd to see the big race and witness the epic celebrations afterwards, but the difficulty I'm having is figuring out how we can get back into Florence later that night. The race is at 19:45, but the last bus out of Siena appears to be at 20:30 -- far too early unless we want to run to the bus station immediately after the race, which kind of undermines our reasons for going to Siena in the first place. The train appears to be no better. So unless buses and/or trains run later during the Palio, which I would kind of expect but is something I haven't been able to find any evidence for, public transportation isn't a possibility.

Overnight accommodation seems to be the obvious solution, but it too seems not to be feasible, for two reasons. First, it looks to be pretty unlikely that anyone would rent us a room for the 2nd only, considering hotels enforce a minimum-stay requirement during the Palio. Although being able to watch the build-up to the race would be both exciting and enjoyable, none of us have ever been to Italy or even Europe before, so there are also plenty of other places that we want to see during our two-week trip as well. Spending three or four nights in Siena, despite its charm, doesn't seem to be the best way of using our scarce time in Italy. Second, camping looks like it could be a possibility, particularly for my sister and I who are younger, not to mention we actually enjoy that sort of thing. Our parents, however, are older, so spending the night sleeping on the ground isn't really an option for them.

There are two other options I can think of, but these also don't seem to be feasible either. The first is to take a taxi back to Florence, but from my cursory search of the internet it looks like we could expect this to cost somewhere around the range of €150-200, which is clearly insane. The second is to rent a car, but driving in Italy, especially into a city like Florence, seems like a bad idea. This wouldn't really be feasible anyway, considering that we'll of course want to enjoy a few celebratory drinks with the winning contrada.

It looks to me like we've exhausted all of our options, making the trip into Siena for the Palio seem to be impossibly impractical. I'm hoping that some of the more learned travellers here might have an alternative idea that we haven't yet considered, or perhaps some of you are privy to some information I'm not aware of.

Your travel advice would be most appreciated,

Minced Grapes.