I had very delicious and reasonably priced meals at these places:
Promessi Sposi (4367 Cannaregio, Calle dell'Oca)...garganelli pasta with fish, tomatoes and capers, and prosecco. (We went here on recommendation of a local worker my friend had stopped to ask directions to another place.)
Casin de Nobili (Dorsoduro, just off Campo San Barnaba)...pasta with veggies, sausage and saffron. Two of us split a big salad of lettuce, arugula, tomatoes, mozzarella, olives, corn, smoked ricotta and baby artichokes. For dessert, tiramisu with peach and bitter biscuits. All this for 30 euro each, including 1/2 litre of red house wine (a merlot), cover charge and tip.
Vedova (6912 Cannaregio, Ramo Ca' d'Oro). I had (melt in my mouth!) liver and onions Venetian style, served with polenta, and a side dish of grilled vegetables. We also had wine, plus biscotti and vin santo for dessert.