You can stretch one chicken a looooong way. Roast a chicken and a veg (carrots, say) and do chicken, carrots, and bread/rolls for dinner one night. Then pull chicken off the bone and make stock from the carcass ( I use the crockpot). You can do chicken tacos, chicken and rice or noodle soup, chicken stirfry, chicken salad, etc. when we're in a lean time the proportion of fillers (like rice or beans) goes way up. Sometimes I will skip the "first night " dinner and head straight to the stretcher meals!
Also don't overlook breakfast for dinner! Scrambled eggs and from scratch pancakes are cheap, easy (can even freeze the pancakes) and would generally not require a trip to the store