Note: often fasting means you eat more after the fast, you end up eating the same amount of food, it mostly just changes when. Don't go to extreme answers.

Along with eat cheap and healthy - $150 is a good amount for food. The issue is usually it means you are trading time for money - the more "from scratch" you make something, the cheaper it is.

The starter point is to look at getting lots of rice and beans - those two together solve a lot of dietary issues that come from moving to a restricted/new diet.

Being able to change things on the fly is also super important - many will say go to the grocery store with a plan. While this can help, I find the plan has to be open to change. Eg. something is on sale for super cheap, you can change your meal plan to include it.

Meal prepping can be done pretty cheaply as well. The raw ingredients for a big ol thing of chilli are actually not that expensive (dried beans, whatever veggies are cheap, can of tomatoes, check out some recipes online). Then you can make lunches for a week, or at least a few days, at a very low cost.

Just a few tips to help you out!