For $80/month, you'll need to treat meat as an occasional treat, rather than a primary meal component.

Stock up on grains such as whole (or steel cut) oats, brown rice, quinoa, etc. Single servings of these grains are about 1/4 cup, so a bulk package (which is cheap) will last a long time. That will be your primary calorie source. Then keep a stock of frozen vegetables such as spinach, carrots, brocolli, etc. Buy these in large generic packages and use liberally in all meals. Eliminate all liquids except water. Buy fresh onions, peppers, potatoes, and sweet potatoes. Finally a dozen eggs a week will provide whole proteins and replace meat as your complete protein source.

Finally legumes (beans) are your friend. Learn to cook batches of dried beans (lentils, chick peas, pinto beans, etc...) and add them to other dishes.

Go to the library and get a couple of books on vegetarian cooking/lifestyle and start learning to cook using those recipes as a guide. Spend a little of your food budget each month to buy spices which will help you add flavor and variety to your food dishes.

Foods high in soluble fiber (whole grains and vegetables) should help alleviate diarrhea problems, but if you've been eating frozen bricks for meals it will likely take a little while to adjust, so you may have to grin and bear it! Just remember to drink plenty of water (6-8 glasses a day at least), since the fiber can cause constipation if not accompanied by enough water.