Thanks for your advices; I hope share the trip with
some of you.
I began a page to coordinate
https://wikimania2013.wikimedia.org/wiki/Wikitrain
Regarding the prices of the train I found it is very (very) varying,
from 150 € to 4300 €, and depends of many parameters like if it is a
global ticket or tickets for local sections, if you buy it on the Web or
in train stations, if you speak Russian, the period in the year, etc. so
a deeper investigation is needed.