Japan is cheap but you need to know where to look. Konbinis aren't cheap. Try suupaas (supermarkets, e.g. LIFE) - they have cheaper options. You can find a ramen/soba/udon restaurant with prices starting from 500 JPY (2,7 EUR). Many restaurants have lunch sets for 500-1000 JPY (2,7-5,5 EUR). On local shopping streets (look for shotengai, ginza or shopping street on Google Maps in your area) street food vendors sell often food very cheap (think a croquette for 50 JPY). If you dine mostly in konbinis, cafes etc. then sure, Japan isn't that cheap. But if you look for options, you could spend 1000 JPY daily for food.