Best visa option for long stay?

Question

I am going on a business trip for 6 months early next year and I am trying to figure out the most preferable visa to allow my girlfriend to be able to move out there with me (neither of us have been to Russia before and never applied for a visa). It is tricky as work is completely doing my work permit so I am not too sure on the procedure either.
We have been told a private (or guest) visa will be the best option when speaking to the consulate for advise but I just wanted to see if this is the best option.
I have read on this site that you can chose visa types based on cost, length of application, etc. and a business visa has been mentioned a lot, the type of stay you actually plan on doing doesn't matter as long as the paperwork ties up. However I have been led to believe that this type of visa requires the person to have a certain amount of backup cash in the bank per day they plan to visit (example: say £100 a day for 10 days, therefore requiring £1000 to be granted the visa).

Thanks

Mark