as others have argued, you do not need to replace the rice with equal amounts of more expensive vegetables. but you replace a small amount of rice with vegetables for the same value as you can afford it. of course it also helps if there is more support for growing the vegetables.

i am in a developing country now. what i have observed is that people here eat more than twice as much rice or other staple food in a meal than i do myself. i suspect that this is to make up for the lack of nutrients they could otherwise get from eating more vegetables.