Eggs, peanut-butter, cottage-cheese, yogurt, milk, nuts, cheese, hummus, beans, and smoothies all have protein and can stretch a budget.
I raised on meat-lover and one vegetarian and I have no idea how it happened. My veg and meat-lover were fed the same diet, but dd just one day stopped eating meat. It took me years, but eventually I gave up trying to get her to eat it.