This is pretty much how I always eat..
Meat:
Get two of the huge 3-3.5 pound packs of Bell & Evans air-chilled boneless and skinless chicken with the Blue label at Whole Foods, they're like 14-15 bucks a piece (for the thighs. There's like 9-10 thighs in each). That's all the meat you'll need for the week, pause. Every other week you can switch to breasts, they run about $22-25 for a huge pack, same brand.
Drink:
Buy 10 gallons of water. Depending on the water you get, you're looking at 15-20 bucks.
Carbs:
Buy a big ass bag of potatoes (prefably organic). There's usually like 10 potatoes in there. That's like 5.99 for the organic bag. Also, get a big ass box of Instant Success Jasmine rice. You'll have to go to another store since they don't have it at Whole foods. Like 4-5 bucks.
Vegetables: Whatever you like, veggies usually run cheap, even the organic. I love okra, they have fresh okra in a pack at Whole Foods, 5 bucks. I run thru like 3 of those a week.
Etc...
Get a bottle of Extra Virgin Olive Oil (You can google the health benefits) to cook with (cook at a moderate temp). That's like 10 bucks.
That's not even gonna be $100. Super healthy, super good, not much money. I don't really ever mess with red meat at all and I don't like fish...you can replace the chicken with some wild caught fish or grass-fed beef or whatever if you want, I've seen big ass packs of frozen Wild Caught fish at Whole Foods for around the same price as the chicken is
And if you're trying to get healthy the diet is most important but you still gotta put in that physical work, hit the gym too champ.
Good luck.