I always keep a package of dried beans on hand and it makes a cheap and filling meal for under $3.
Soak the beans for a few hours, rinse then put in the crockpot/slow cooker with water. I don't use the flavor packet that comes with the bean soup package, instead I either add a package of taco seasoning or make my own.
Taco Seasoning
1 tbsp chili powder
1/4 teasp. garlic powder
1/4 teasp. onion powder
1/4 teasp. crushed red pepper flakes
1/4 teasp. dried oregano
1/2 teasp. paprika
1 1/2 teasp ground cumin
1 teasp. salt
1 tsp black pepper
Note: This seasoning is quite spicy/hot. You could limit the amount of chili powder and red pepper flakes or search online for other suggestions