I did Jenny Craig a couple of years ago and the main reason I quit was that the food cost so much. It was about $300 a month. I talked to the consultant about ways to get it to cost less. Of course, she discouraged not buying the snacks or making my own breakfast because she got a commission from everything I bought. She did say I could use all "shelf-stable" foods instead of frozen. They had some canned soups, tuna and cracker kits, dry cereals and non-frozen dinners. I didn't really like their food but the shelf stable was the worst. I couldn't imagine living on it for several months.
Besides just buying their food, you have to supplement with foods you purchase yourself like fruits and vegetables, yogurt, etc. You need to add these extra items in when calculating how much the entire program will cost you.