I got my Russian visa from a company called Intourist, who are the ex-Russian Tourist Board. We used their Glasgow office, I would avoid using the Glasgow office as I had to deal with a girl who was absolutley useless. The manager in Glasgow was very good, or use the London office.
This is their website
http://www.intourist.co.uk/intourist/itmainsc. php
It took about a week. Intourist charged �60, the actual cost of the visa was �30.
You need to ensure that all paperwork is correct. You need to know your arrival dates, and departure dates. If these are different to when you actual arrive, you're not allowed in.
Not sure how easy it is to get a visa with out going through a company, as you need a letter of invitation from a Russian business.
I applied for Russia, Mongolia and Chinese visas and was told that the Russian one was the hardest to get.