Sardines and mackerel. Both inexpensive and sustainable. Sardines are a terrific replacement for anchovies on a Caesar salad (less salt). Canned mackerel makes a great fish patty. One can plus 2-cups of oat flour, two eggs, seasoning of your choice. I use garlic, crushed red peppers, salt and Parmesan. Mash together until mixed well, add enough flour to make into a ball, fatten to a patty and fry in olive oil. Make two big patties.