Pasta is very cheap and filling and one pkg makes a lg quantity, not sure about how loaded with nutrients though.
Canned veggies are also very cheap and make great side dishes. Such as
1) mix of corn and pickles with mayo and garlic.
2) Saute canned green beans with an onion soy sauce and garlic
3) Beans are full of protien, so adding canned beans to a soup make it flavorful and full of protien.