Reasonable sushi run by a fish store in Okachimachi
Just near the Okachimachi (御徒町) JR Station and Ameya-Yokocho (Ameyoko, アメ横）, I found a reasonable sushi restaurant named "Syun Okatimachi(しゅん 御徒町)" run by Yoshiike (吉池), a big fish store. A big lunch set meal costed just JPY1,300. The price setting at lunch seems equivalent to that of sushi-go-round restaurants, but here, sushi chefs cook at the counter.
Lunch meal (JPY1,300)
Considering the price, you shouldn't have excessive expectations, but If you plan to have sushi at Aymeyoko where fish is sold, I recommend Syun instead (actually, there is no good sushi restaurant there...). You can be full by the set of JPY1,300! My rating is 3.4 out of 5. Gochiso-samadeshita!