One of my favorite cheap meals has always been sloppy joe barbecue or saucy green beans over baked or mashed potatoes.
My grandmother used to make a side dish by sauteeing bacon and onion and adding canned green beans and tomato sauce. She'd serve it over mashed potatoes with some type of meat or meatloaf. If she didn't have bacon, she'd dice up balogna or hot dogs.
In college I lived on the sauced-up beans over baked potatoes.
If I'm lazy, I use a jar of Aldi brand mushroom spaghetti sauce (99 cents for a large jar, about a quart of sauce, I'd estimate) and a couple cans of french style green beans (2 cans for a dollar at the Dollar Tree).
Today I wanted mashed potatoes and barbecue, so I made a huge pile of mashed potato/cauliflower for only 1 starch serving, 2 vegetable servings and 1/2 of a dairy serving (about about 175 calories).
I used low-fat (1 can) of chicken broth to cook 4 cups of cauliflower (From a head of cauliflower, I used all of the core and enough cauliflower to make 4 cups), until tender. I added one fresh garlic clove (dried garlic or garlic powder works fine too, but i usually add that at the end). I cooked it uncovered, so a lot of the broth evaporated by the time the cauliflower was tender. Then I added 1 cup of skim milk and when the milk/broth began to bubble, I added 46g of dry mashed potato flakes (I used my food scale, and used what was listed on the box as the amount of potato flakes to to make two servings). I have added butter, but it turns out pretty weill without it too (especially when made with the chicken broth).
This made a HUGE pile of cauli-taters. I chose half as my serving, but it was a big pile.
The barbecue chicken was actually left over salsa chicken (chicken thighs cooked in cheap salsa in the crockpot). I removed the bones and shredded the chicken with a fork. I sauteed in a pan with a bit of water, bean sprouts and a can of frensh style green beans and added splenda and seasonings.
Basically, it's a variation of my "stretched" sloppy joes, where I'll add shredded cabbage, green beans, or bean sprouts to add veggies and dilute calories. It works for sloppy joes, stir fries, spaghetti sauces any "saucy" recipe can be stretched with mild flavored shredded veggies.
Cheap, tasty, filling, low-calorie, and easy. It's a pretty rare combination.