Aeroflot is cheap, and other Russian airlines. Flying through Moscow with anything but Russian airlines is not as cheap as one would expect. The reason is that Moscow has decided to limit the amount of permits that would allow an airline to operate within it's airspace to one per country. Flying over Russia would be the best choice when flying between Europe and Asia cost wise if not for the limited availability and cost of the permit.

And please, don't be allured to Aeroflot due to the cheap flights, it's not an experience worth having.