It is possible to survive on a food-stamp size budget and keep Kosher. I know because there have been times in the past I have had no choice but to do so. It’s not a lot of fun and it’s not the healthiest, but you can survive and avoid starvation. You go heavy on eggs and tuna, bread, rice, potatoes, pasta, beans and cheap canned vegetables. Use very tiny amounts of chicken and ground meat (like a quarter pound of ground meat to feed 8 people) to flavor the carbs. There have been plenty of Shabbosim when I used less than $5 worth of meat in a cholent that was mostly potatoes. It’s not what you want to do, but some Yidden don’t really have any other choice.
Today, B”H my grocery budget is higher.