There are websites where you can get this document electronically quickly and for less than 10 euros.
A web page that quickly get the visa support and referred to in many blogs Destination travel is Russia. On this website costs about 16 euros an entry visa. In the form you can see all the hotels by cities.
But the choice I've used it recently has not been this but in Hotels Pro. This is a Russian company registered as a tour operator whose business is based on the emission of the support visa in transportation services and ticket sales tickets.
This company offers to each of its partner hotels reservation system itself. Depending on the hotel you access the associated costs vary. The cheapest I've found on the website of visa management Googol Mogol Hotel St. Petersburg. You perform the procedure for 600 rubles (about 9 euros at the current exchange rate of 1 euro / 65 rubles) and in less than 24 hours you will have your invitation letter by email ready to print.
To get you to enter their website: http://hotels-pro.ru/order/gogolmogol
took information from here www.rusalia.com/tramitar-visado-viajar-rusia