Not single, but I cook for one a lot.
I find that the grocery bill runs high if I buy too many convenience foods. When I was initially diagnosed with type 2 diabetes I relied on microwave meals to make my life easier with transitioning to a new diet. (Twice a day =$6 =$84 per 2 weeks). I have since cut back to microwave meals to just once a day (and will eventually ween off completely).
I now look for staple foods that I can make many things with and try to stretch certain foods that are the expensive healthy options. For example, I bought wild grain rice which is lower carbs than white or brown rice. $4 for one tiny box which is supposed to be 2.5 servings. I split it into 8 portions to put in my burritos (I eat burritos instead of sandwiches).
And because of other diet restrictions, I have cut out other higher priced items like lunch meats and cheeses. Instead I buy chicken breast and cook it up and dice it to use in whatever I'm making. Five large chicken breasts for about $6 instead of one package of shaved chicken for the same price. I had 8 half cup portions and it is a lot healthier than the lunch meat without preservatives and extra sodium. (I'm supposed to watch my sodium intake).
So I made enough filler for 8 burritos. Mostly relying on fresh ingredients
Wild Rice - $4
Low sodium black beans - $1
Boneless skinless Chicken breast - $6
Red and green bell pepper (one was free from my parents' garden) - $1
Onion - $.25
High Fiber Tortillas - $5
8 Burritos = $17.25 ($2.15~ each) (About 500 calories with guac and salsas) Cheaper and healthier than the pre-made microwave meals and it took me less than 30 minutes to prepare. I divided out portions in separate containers and now all I have to do is microwave it for 30-45 seconds and I have a quick and easy meal.