Please note: the dollar amount in these articles generally refers to the USD, portion sizes and will vary from place to place.
Here's some articles that might help you:
1) From the Dieticians' Association of Australia:
2) 15 foods for about $2 from WebMD:
3) Tips to eat well on a budget from Huffington Post:
4) 44 Nutrient dense foods, under $1:
5) Family food on a tight budget:
Circumstances are different for everyone. It's difficult to cook everything if you do not have access to a kitchen and it's difficult sometimes to prepare everything from scratch if you are unwell. It's harder to stick to a budget if your diet is restricted due to allergies. This is just a list of articles that may inspire you.