You can extend a Russian visa if you get an invitation from a Russian organisation or citizen. If you have a ticket for a train that departs the next day you can stay overnight in a station dormitory. The price is around R30,000-40,000; almost every station has dormitories.
We were given an eight-month tourist visa from the consulate in London (5 Kensington Palace Gardens) for only 10 Euro. It would appear that an eight-month tourist visa is unusual but it was issued without any question. (We had obtained an invitation from Travel Russia in Moscow.)
