www.skyscanner.net for all your flight needs. Don't be afraid of booking a flight that sees you staying the night before somewhere outside Russia - will save you on hotels and beer costs!
As for Visas, apparently the Russians are planning something for independent travellers, if not there are reputable agencies out there that will do all the leg work (including invitation letters) for an all-in fee of about £90 and can turn things round in a week.
Make sure you get stuff booked up before the scousers/cockneys though! Leave those fuckers with nothing under a grand!
