One of my the best and cheapest(!) street food experiences happened last week at Ameyoko shopping street. "Ame" stands for America as a lot of American products were available at this former black market area after World War Two.
This filling bowl of rice with scallops and roasted fatty salmon, + miso soup and complimentary tea costed about 4€, proving that it's possible to experience and get the best out of Tokyo even when on budget. Compared to Estonia, I think it so much easier to find great and very cheap lunches here.
Also, yummy takoyakis (octopus balls) were made right there. My ultimate comfort food!