If you travel Hakodate, Hokkaido on a tight budget, why don't you try one of the "500 yen don" or 500 yen rice bowls at the morning market just next to the Hakodate Railway Station?
There are many restaurants to serve fresh seafood at the market, and I found a place serving a bowl of rice topped with fresh seafood for just 500 yen among other places charging nearly or more than 2000 yen.
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Gomoku or Mix don (upper left); Salmon roe don (upper right); Crab meat don (lower left); the restaurant, Ekini Shijo located upper floor (lower right)
I think you'll like them if you like sushi. There is no menu in English, but Japanese menu carries pictures of each rice bowl, so you can order just pointing a picture. Served with miso soup and pickles. Opens 6:30 AM till 2:30 PM everyday.