Tempura Hisago may not be the best tempura restaurant in Tokyo, but their lunch is reasonably priced (around 2,000 yen) and filling enough to last you until the next morning. They serve very decent Edo-style tempura. Personally I wasn't able to finish my dessert, matcha ice-cream, because the set consisted of too many dishes.
Tempura Hisago is a chain restaurant which also has a branch in Akihabara. We visited the Ginza branch, which is conveniently located on the 12th floor of new Mitsukoshi building. The majority of customers at lunchtime are elder women.
Lunch time is from 11am to 4pm (last order at 3:30pm) and dinner time is from 5pm to 11pm (last order - 9:30pm), but you can expect to pay 6,000–8,000 yen in the evening. If you like your tempura piping hot, opt for the seat at the counter.