Best route: Paris to Florence (Sienna)

By train, it's 12hrs on the Thello night train to Florence. A compartment with 6 couchettes (you have neighbors) is a low as 35Euro. A compartment with 4 couchettes is as low as 55Euros. By plane, you can fly from Paris-Orly to Pisa in about 1hr45min. I see fares as low as 45Euro on www.easyjet.com. From the train station at the Pisa airport, you can take the train all the way to Siena without going through Florence. Journey time is about 2hrs on the faster runs and about 2.5hrs on the slower runs. Fare is as low as 9.80Euro. A mandatory train change at Pisa Centrale and most likely at Empoli. Or, you can go to Florence, walk about 300 meters to the SITA bus station and take the bus to Siena.

To supplement Larry's excellent specific advice: The Bahn website is the best one for train schedules and routes. It will not have prices for trains outside of Germany. For trains leaving from France, use the TGV Europe site, choose Great Britain as your country, and resist all entreaties to go to Rail Europe (either the US or the UK one). For trains within Italy, use the Trenitalia website. For finding flights within Europe, use http://www.skyscanner.com.

There are 3 ways: 1- Drive Paris-Florence approx. 750 miles (about 12 hours if you don't stop too much) 2- Night train Paris-Florence. Approx. 14 hours. A couchette in a six unit compartment starts at Euro 35 and up. If you want your own bed compartment I think it's at least 200 euros. 3- Fly from Paris to either Florence or Pisa, then bus or train to Siena. Flying options are below: PARIS CDG - FLORENCE FLR - AirFrance (6 daily pairs) PARIS ORY - FLORENCE FLR - Vueling (1 daily pair) PARIS CDG - PISA PSA - AirFrance (3 daily pairs) PARIS ORY - PISA PSA - EasyJet (1 daily pair)
PARIS BVA - PISA PSA - RyanAir (1 daily pair) From Florence to Siena it's quicker than from Pisa to Siena, however not by a whole lot, therefore you should look for the cheapest and most convenient flight. Please consider that Paris BVA is in Beauvais, about 1 hr. from Paris.

Wow. Awesome tips all the way around! Thanks everyone! Sounds like there's no easy, direct way of getting there, but at least it won't be all that expensive.

Roberto's flight advice is the best. You'll want to end up at the Florence train station to catch a bus to Siena. Trains dump you to far from the center of Siena. You turn left in the Florence train station and go out south end of the station. Across the street is a McDonalds. The buses are lined up to the right of the McDonalds around the corner and around the block turning left. If you're wanting to visit numerous hill country towns, just rent a car in Siena and ramble throughout the Tuscan farm country. Roads are easily negotiated in the area, and you'll just see so much more of the region.

Max, One of the easiest and most direct methods on that route is a budget flight from Paris to Pisa, and then train to Siena. Of the options that Roberto mentioned, I'd suggest EasyJet from ORY to PSA. They currently have flights listed as low as €44.99, but the price will vary according to which flight you choose and how far in advance you book. There will be a few "fees" with any of the airlines. Be sure to read their Terms & Conditions carefully, especially relating to baggage weights. Note that usually only ONE carry-on item is allowed. One advantage with Pisa is that there's a station right at the airport. Travel from Pisa Airport to Siena is relatively easy. The trip is about 2H:20M, often with two changes at Pisa Centrale and Empoli. Many of the trains on that route are Regionale, so DON'T forget to validate your ticket prior to boarding the train! Current Second Class fare is currently indicated at €9.80 PP. For flight information, check the EasyJet website. For rail travel information, check either German Rail website or the Trenitalia website. Happy travels!

I don't totally agree with Ken on the flight options to Pisa. I don't know when you are traveling, but you can fly with Vueling from Paris ORY directly to Florence FLR (non stop) for as little as 39.99 Euro in January. I also checked as far ahead as June, which is high season, and prices, even in June range from 59.99 Euro to 79.99 Euro on the more expensive days. From Florence airport you can take a SITA/ATAF bus shuttle to the station that stops near the SITA Autostazione in via Santa Caterina Da Siena. A bus will take you from there to Siena on top of the hill right in the city center (rather than the station at the bottom of the hill). I had to present you with all the facts and I will make full disclosure that I'm from Florence and we Florentines have been at war with Pisa for centuries and we still don't like one another.

@Roberto, I agree that a Vueling flight from ORY to FLR is also a great option, and I should have mentioned that. Overall, the travel time from Paris to Siena, either via Pisa or Florence will likely be comparable. I should also mention that I tend to favour EasyJet over others, as my experience with them has always been "easy". I tend to have a bias against RyanAir as my last experience with them was not pleasant.