Did you mean to post this in Travel Buzz? It's not going to get much of a response in the Talk Board forum. Maybe a moderator can move it out of here.
I've done rail when in France, and a flexible pass is pretty reasonable. You can also get a pass to combine France and Italy. You'll just need to sort out if this is cheaper than point to point tickets, depending where you might end up.
http://www.ricksteves.com/rail/france.htm
I just hopped over to Imperia, Italy for a few days from Menton in France (pretty close to the border), and bought a local Italian ticket to supplement my French rail pass. That worked out fine if you wanted to jump over to Italy.
Nice to Monaco is as little as 13 mins by train, depending on the type of train you take.