OK Larry - kinda right :)
Joel - the prices I quoted you are, as I said in my post, are ALL AMICA 2nd class tickets on Eurostar. As Larry points out (correctly), there are many other options you can take.
If you have kids (12-26), you can spend 40 euros and buy a Carta Verde and get discounts on their travel. If, like me, you travel the trains a bunch you can join the TernItalia Society and earn points for your travels and get discounts! So the prices I quoted you are generally the quickest, fastest, cleanest, and most comfortable trains on the line.
Tickets are available only 60 days in advance but fares do not change very often so you're safe plugging a 59 day option just to get an idea!
Like booking a plane ticket, there are multiple options available to you on the Italian (and European) train system. Best way to approach it is to go to the website and DIG! Once educated, head to the train station with your best options and price that fits your travels!
Good Luck!
Ron