You're right, the procedure for getting an invitation,visa, etc for Russia seems convoluted. However, it was made considerably easier for us when I booked a hotel over the internet through moscow-hotels.net. They faxed me a letter of invitation (free) which covered the whole trip, which we then submitted to the Russian consulate with our visa application. It is my understanding that the Consulate will not give a letter of invitation, it has to come from an agency or hotel in Russia and many of them charge a fee. Are you considering Moscow? It is quite different from St. Petersburg and only an overnight train ride away.

Regards, Dolores St. John's, Newfoundland