learn_russian | В Россию-- вперед! (с многих денег?)

Entirely unrelated to this community, but I find that the members here are quite helpful and knowledgeable, so I'll give it a go:

Looking for travel options from the UK to Russia (Moscow) in September (TO LIVE NOT BE TOURIST), I'm seeing they cost roughly £150-£300. However, I've heard that it's "much cheaper" to just fly to a major Eastern-European hub inside the EU like Warsaw, Riga or Talinn and actually go into Russia by train. Is this bollocks? £200 isn't cheap by my standards, but it seems pretty cheap for a long flight like that. I have no clue how expensive/cheap a Polish long-distance train might be.

Finally, Russians always seem to tell me that "Russia/Moscow is one of the most expensive places in the world". Coming from a place like the UK, them's fightin' words. How bad is it, really? I mean, what kind of budget should I prepare as a student (who's only drunk ~1 night per week)? I don't want to end up on the street/starving/perpetually sober, especially in Moscow.