What groceries are fine to buy as cheap as possible without it being unhealthy? (Cw: possible talk of animal harm)

Like, I know most chicken is grown in the most unsanitary conditions possible and it can’t possibly be healthy to buy the standard stuff at the grocery store (or is it?).

What about fruits and veggies? Can I just buy that stuff at the cheapest store without it causing more cancer than the higher priced options?

Trying to find the perfect combination of cheap, nutritious, and bereft of microplastics.