i think you can eat it more than twice per week. there may be some concern over the mercury, but if you make sure you're getting a lot of selenium you should be fine. i eat sardines pretty much every day for my omega balance. speaking of which, remember that the goal is to get a 1:1 balance, so if you are going to eat a lot of fish, throw in some eggs or chicken in there too for some omega 6.
how is this cutting your food costs? beef and chicken cost a lot less per pound here than fish. if i could afford to eat fish (other than a can of sardines) every day i probably would.