The Eurostar train between Rome and Florence now costs two and one-half times that of the slow "Regionale" train: 39.90 Euros versus a mere 16.10 Euros. Both fares are for second class. Travel time is 100 minutes on the Eurostar versus 230 minutes on the "Regionale."
A "compromise" solution is to take one of the "Intercity" trains, which cost 26.50 Euros in second class. But MAKE SURE that the IC goes to Firenze S. M. Novella Station and not just to Firenze Rifredi Station. Travel time on these trains averages 170 minutes. They make four or five stops enroute.
BEWARE: MOST of the IC trains DO NOT stop at S.M. Novella Station.
COST SAVINGS: Four adults travelling together will save nearly 100 Euros by taking the Regionale versus the Eurostar!!!
Remember that there are no seat reservations on the Regionale train. However, if you board early in either Rome or Florence, you should have no problem finding a seat.
HINT: Pay 50% more and travel in a much more comfortable first class seat on the Regionale. It still costs much less than second class on the Eurostar. First class seats are wider, plusher, more comfortable (soft cloth fabric versus hard and sticky vinyl with rubber frames in second class), and they pivot forward for a modest recline (whereas second class on the Regionale does not.) There is usually only one first class railcar per Regionale train.
BEWARE: The Regionale train makes 17 stops between Roma Termini and Firenze S.M. Novella Stations. This is truly the "slow" way to travel between these two cities in Central Italy!!! By contrast, all of the Eurostar trains (save one, which stops at Arezzo) travel nonstop between Rome and Florence.
NOTE: Many travellers will elect to travel on the Eurostar because their limited vacation time is more valuable than the time lost by taking the slow train.
NOTE: The Regionale trains should all have heating and air conditioning, but there is no food or beverage service on these trains.