Need help with the schedule and cost of train from rome to venice to florence and back to rome again in nov..?

GuFo is right schedules and prices aren't published that far in advance. There may be some modifications, but what you see now should be fairly close. Your plan looks pretty good - especially getting back to Rome the day before your flight. One thing I would suggest that you consider is the night train from Rome to Venice. It's a little cheaper than the fast trains and you won't need a hotel for the night. Since you travel during time you're normally sleeping anyway, you'll be able to maximize the time you have to do some sightseeing.