Russian Federal Customs Service reports that in January 2013 the amount of the federal budget, administered by the customs authorities of 410.76 billion rubles.
I want to remind you that the average for the previous year is 540 billion rubles a month. Thus a drop of 25%! on average.
For the whole year, I only saw a drop of up to 510 billion in one of the months in the fall of oil prices by 20%.