Not such a perfect way to find some acceptable searching for realy "budget" places. In Moscow I'd like to recommend midle-prices places:
Mama-Tao (good chineese food) - Pyatnitskaya str.
Grabli (russian/european cuisine) - Alekseevskaya subway st.
Budget food is often located in food-courts in big supermarkets:
Kroshka-Kartoshka (hot potato with different salads)
Melenka (russian pankakes)
Rostiks (russian KFC-like food)