sadly the cheapest meat are the “name brands” with nitrates in it. you can buy cheap sandwich meat from trader joes though.(instore brand). going vegan might be harder, as you will be nutrient deficient(you need supplments to compensate like b12).

Hummus on its own or any and all parts of lettuce, tomato, rocket, roast peppers. Om sourdought foccacia is phenomenal

It depends on what your local store has at best prices, really. Depending on where you are, you might find anything at a locally better price.

Famously, though, the absolute cheapest sandwich that some people still love is a salt&pepper toast sandwich, literally softened butter on bread, toasted if you have a way to toast it, or maybe fried, with a sprinkle of salt and pepper, stuck between two other slices of bread. I have made it before and it’s way better than it sounds. If you’re wanting to push the price as low as possible, the salt and pepper might be gotten from fast food places’ condiment stations, maybe even the butter/margerine as well if you have the right kind of place.

A mash sandwich is also deceptively good if you make good mash or have good condiments, and skin-on potatoes are almost always good nutritional value for money.

Beyond that, almost any sandwich can be bulked out with leafy greens for not much cost. Great iron in spinach. Lettuce other than iceburg is mild and nutriticious so helps almost any savory sandwich. Fiber helps you feel full too.

If you have an air fryer, tofu slabs!

Slice a block of tofu short-ways into six to eight slices. Season on each side with oil and choice of seasoning. I use adoboe seasoning, garlic salt, paprika, and other savory flavors. Lay in a single layer in the air fryer and fry for 15 mins at 400 F, flipping with tongs halfway through. Put on bread, add condiments if you want, and eat. Leftover slices can be put into the fridge and either reheated or eaten as cold cuts.

Where I am, this works out to less than a dollar per sandwich, and makes a complete protein. Add some lettuce and tomato or other veg for more flavor, fiber, and vitamins if you can swing it.

Idk if you go to Costco but I get a $5 rotisserie chicken.

If you have access to a hot pot or oven, braising your own meat will be cheaper than cold cuts. Pork, whole chickens, and parts of turkey will be cheaper by the pound than their equivalent meat as a cold cut.

Mashed chickpeas with vegan mayo is a good approximation of a tunafish sandwich.

Toast sandwich

Zero carb tortillas / pizza sauce / cheese/pepperoni is super cheep pizza.

Cast iron pan / fresh green beans / butter / garlic

Chicken / rice/broth soup

Rice is super cheap and can be used with a combination of ingredients. And makes quite a few meals. I miss being able to eat rice.

Zucchini sliced, green pepper, red pepper, onion, andoulie sausage if you can afford it. Coat in Italian seasoning or slap ya momma.

Air fry for 15 minutes. You can easily get two meals out of that

Tomato. PB. Egg.

Op post a budget and how many days you need it to last. That’s far more helpful.

Also what do you have to cook in? Stovetop? Oven? Microwave? Air fryer? Crockpot?

We can be far more helpful if we know some details

Peanut Butter. As a diabetic it’s my go to when I want something sweet. As long as it’s natural.

Also I don’t know your kitchen situation but you can live off just Potatoes and they’re filling. Microwave, bake, or air fryer. They are awesome in air fryer.

But how bad off are you if you can’t even get cheese slices?

Like what’s your budget? How many days before you get paid and how long do you need a extremely tight budget for?

Peanut butter is one of the cheapest shelf stable foods, either per calorie or per gram of protein. It’s obviously delicious with some sort of fruit jelly/jam. And the protein in peanuts complements the protein in bread, covers all the essential amino acids.

Spreadable or meltable cheeses are pretty delicious on toast, and can be supplemented with seasonings. I put cream cheese and everything bagel seasoning on my sourdough slices most mornings.

There are also a ton of delicious toppings for open face “sandwiches” or toast:

1. Avocado is a classic for a reason. If avocados are cheap near you, that can be an option.
2. Fresh tomatoes on toast are a classic in Spain for a reason, too.
3. Sardines or other canned fish/seafood, if you like that.
4. Mediterranean spreads like hummus, baba ganoush, muhammara, harissa, etc.
5. Shrimp, like gambas al ajillo or something similar, go really well on toast.
6. Roasted mushrooms

If you’re baking your own bread, you can also try to shape some little bread bowls and fill them with soup. French onion soup takes some time but the ingredients are pretty cheap.

Not all of these options are ultra cheap, but many are flavorful enough that even small portions can work out to be really affordable on a per calorie basis, for stretching that budget with bread.

Not exactly what you asked, but there are whole traditions of non-sandwich food eaten with bread. For example, if you can get lentils for cheap you should look into lentil soup, and same for broad beans and ful. Also you can put a thin layer of tahini on top of molasses for a surprisingly tasty breakfast. You eat all these by scooping them up with bread.