The cheapest place to eat hands down is the Bush Canteens. I am not sure if it is technically on campus, but it is at least adjacent to it. For a mere two cedis you can get a large fufu, a piece of meat (chicken, fish, goat, or beef) and light soup or groundnut soup. The only drawback is it is a bit of a walk away from my house and office.
Also cheap and a little closer and also near the grocery store and bank is the night market. You can get a couple scoops of jollof rice, a piece of chicken, salad, sauce, and pepper for between two and four cedis here. So far I have avoided buying a rice cooker because cooked and seasoned rice is still quite cheap here.
Wiltex is the closest place to eat from the history department. The most expensive thing on the menu is tilapia with pepper at four and a half cedis. If you throw in a ball of banku and a beverage it goes up to six. The cheapest thing is the fufu. You can get two fufus and a piece of goat in light soup for two and a half cedis. Finally, you can get a big plate of jolloff rice, fried rice, sausage in gravy, sauce, spaghetti, chicken, and steamed cabbage for less than five cedis. Their pineapple juice goes well with everything.