The opinion is that it’s impossible to tell without some kind of itenerary to look at. Obvoiusly you won’t stay put all that time, but will you mainly travel from one major city to another or will you try to see smaler places along the way? Can you make a list of long (longer then, say three hours) trips you are going to make?

For a two or three month trip, the cost of a two or three month railpass is a pretty good estimate of what you’ll spend getting from city to city.  However, a combination of a less comprehensive railpass (or two), some point to point train tickets, a couple of cheap flights and some bus and ferry rides is probably a better way to spend that amount of money.

It’s impossible to know the best and cheapest way to get from city to city without an exact itinerary — with dates — so you can check for cheap flights, point to point train specials, etc.