Check the Republics. Kazan and Ufa.
, in addition to MSK and SpB
There's a deal with the federal government re: airfare tariffs. Also Aeroflot operates and Kazan-FRA flight specifically for the Tatar Government also ( to support industry)
Kazan is worth spending the night btw, if only to check it out.
Also it goes without saying that flights from Russia to the "territory" of Crimea is also attractively priced for the local market.