Generally you will be ripped off. One that I CAN recommend, where you will get a fair price is along Fondamenta San Giobbe, on the north side of the island.
But just generally, be careful of what they put on the table, bread is not always free. Also, check the service charge (coperto) before you go in. Some places charge exorbitant amounts!
Also, do not eat along the Grand Canal or on St. Marks Square, the price there is usually 2 or 3 times normal Venice prices which are expensive to begin with! almost 8 years ago