It can be very hard to eat a healthy diet if you're poor or if you live in a food desert, or you have a dietary restriction, or some allergies...
You can prepare healthy meals from basic and cheap foodstuffs like vegetables, whole grains and legumes, eggs, low cost meat cuts etc. You can prepare delicious meals for under $1 each.
Buying prepared unhealthy foods is what is expensive.
Being poor is very expensive.
> You can prepare delicious meals for under $1 each.
If you have the time and resources to do so.
Many poor people literally do not live near a grocery store, the only place they can get foodstuff is a convenience store. Those always have high markups