Flights are Outrageously expensive. My girlfriend (US citizen but born in Russia) was looking to go in August to visit some friends. They were $3,000+ via IST and required like a 30 hour layover. As mlin32 noted, you also won't be able to use any of your cards (including your debit card to get cash). That is fine in Cuba where things are cheap, but it would be a nightmare in Moscow.