Years ago I recommended www.travelrussia.su to a traveller from Rwanda (Africa) who has finally made it here this Fall with a visa obtained based on their invitation, and was happy to recommend them. And here I am passing this info on to you. The rate (under $100) seems entirely reasonable, and the service was said to be quick and trouble-free. Talk to them if you are a citizen of one of these places that are on the Russian Ministry of Foreign Affairs’ “migration risk” list.