It should be doable without too much pain after a bit of practice. I second the Costco suggestion, but also shop the sales, no pre packaged foods. Crockpot cooking (inexpensive cuts of meat become tender and flavorful with the slow brasing).
Breakfast cereals are expensive, if he really likes cereal, he can share the pain by foregoing those. Buy the big tup O Oatmeal, or box of cream of wheat.
Ramen is fine – use them as a base in a chicken salad with an asian dressing
If he wants a salad it doesn’t have to be dry (and bottled dressings are expensive for what they are). They can be done by hand, but are easier if you happen to have a blender, food processor, or stick blender. Make homemade salad dressings: oil, vinegar, flavorings. For creamy add some emusisfiers – mustard and egg (buy pastureized eggs if you have health concerns about raw egg useage).
Plan. Cook potroast, its a meal once, hot beaf sandwiches with mashed potatoes next night, leftovers seasoned for tacos and used that way. If you can’t toleratrate that many meals in a row of beef – freeze the leftovers and pull them out next week.
Pre-roasted Costco chicken at 4.99 is a fast meal and as inexpensive as it gets. It’s good for several meals. HOt meal one night, Sandwiches for lunch, chopped as chicken salad then simmer bones with water onion celery and carrot to make your own stock as a base for chicken/dumplings or chicken noodle soup.
Learn a variety of bean and rice dishes (rice pilaf with different seasonings, fried rice, rice pudding) they’re filling and inexpensive and make main dishes go further.
Since your husband is adamant about this, make him help with planning and shopping – especially shopping the sales so that maybe he will understand that sometimes it’s worth overspending the budget to stock up on something that is a great deal.
If possible switch your thinking about this so that instead of being a pain, it’s a challenge/game.