Did a quick search and saw you can take the train from Monaco to Florence for about 36 Euros. The trip takes 6 hours.
We drive but my guess would be the train. I only checked one date and prices ran from 46 to 122 euros. Here's the web site so you can check your real days. http://www.sncf.com/fr/
It would help to know where you want to go in Tuscany. I was using Florence. Other places will be other prices, and time will affect the cost. Best of you put the correct information in yourself.
Enjoy your trip.