Paris to Italy is a short flight.

Yes, 行李要收費. Just don't order any on-board drink and you should be fine. 廉價航空 should be still much cheaper than 火車. The most importan thing is you will save a lot of time by taking flight. You have more time to enjoy Italy. Be careful 小偷 in Paris. We met twice. Once, a group of girls (about 12 - 14 years old) already openned my backpack but did not get anything. We did not have any problem in Italy but we did see police to arrest 小偷. There are a lot of polices in Rome.

Good lucky,

Xiong