And you could get a chicken, a friend for life (or at least 10-15 years if you're lucky).
Everything said up there is pretty dead on, my own 2 cents would be that an extremely frugal and cheap diet of rice and beans/lentils/peas and some source of essential oils (sunflower is ok) , would be essentially enough for most vegetarians to subsist on, provided some variety of other foods is included for vitamins (mostly iron and B vitamins would be lacking from this diet) If you eat some meat you should be fine.
Nuts are expencive but a good source of protien and a very good source of healthy fats, also if you can afford it linseed is probably the healthiest grain/oil you can get, mostly because it's high in omega 3 which most other unsaturated oils are low in. (Though i think if you consume high levels of omega 3 and low levels of omega 6 you'll end up deficient also).
I'm rather fond of fairly frugal noodle/rice soups myself which would fit your situation quite well.
Take some fresh garlic and diced onion and lightly fry in a bit of oil, add diced vegetables like carrot, celery and broccoli and cook a bit, then add dried beans which have been soaked in water for half a day (a small hassle, but you can just take a handful of dried beans and add twice as much water, you'll have enough for a few days), cook untill slightly soft, add water and either noodles or precooked leftover rice.
Season with a bit of salt and pepper. Taking this pretty simple recipe you can add whatever other vegetables or meats you have around, even an egg is a good additional source of protien, or throw in some nuts.
Also learn to microwave rice, it's easy and when you have leftover rice in the fridge you can make a simple snack very easily.
I've recently myself rediscovered the digestive benefits of fruit, i have generally poor digestion and fairly infrequent bowel movement, but lately i've been processing fruit into high pulp smoothies (wash fruit throughly, peel inedible skin and remove seeds,put into food processor and pulp it throughly, combine with about 50% water to improve drinkability and also because the fibre absorbs the water and it becomes far better for digestion, then drink)
Tastes ok, very refreshing and hydrating, and gets things moving smoothly much better than anything, even better than merely eating fruit and drinking water seperately. However i should add that any amount of processing damages certain vitamins, C especially gets damaged from oxidation and is best retained if you eat fruit whole.